When I click after about 15 minutes on a page I wrote I recieve the 
following error:

Server Error in '/' Application.
--------------------------------------------------------------------------------

Validation of viewstate MAC failed. If this application is hosted by a Web 
Farm or cluster, ensure that <machineKey> configuration specifies the same 
validationKey and validation algorithm. AutoGenerate cannot be used in a 
cluster.
Description: An unhandled exception occurred during the execution of the 
current web request. Please review the stack trace for more information 
about the error and where it originated in the code.

Exception Details: System.Web.HttpException: Validation of viewstate MAC 
failed. If this application is hosted by a Web Farm or cluster, ensure that 
<machineKey> configuration specifies the same validationKey and validation 
algorithm. AutoGenerate cannot be used in a cluster.

Source Error:

      The source code that generated this unhandled exception can only be 
shown when compiled in debug mode. To enable this, please follow one of the 
below steps, then request the URL:

      1. Add a "Debug=true" directive at the top of the file that generated 
the error. Example:

        <%@ Page Language="C#" Debug="true" %>

      or:

      2) Add the following section to the configuration file of your 
application:

      <configuration>
         <system.web>
             <compilation debug="true"/>
         </system.web>
      </configuration>

      Note that this second technique will cause all files within a given 
application to be compiled in debug mode. The first technique will cause 
only that particular file to be compiled in debug mode.

      Important: Running applications in debug mode does incur a 
memory/performance overhead. You should make sure that an application has 
debugging disabled before deploying into production scenario.

Stack Trace:

[HttpException (0x80004005): Unable to validate data.]
   System.Web.Configuration.MachineKeySection.GetDecodedData(Byte[] buf, 
Byte[] modifier, Int32 start, Int32 length, Int32& dataLength) +2549692
   System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) +214

[ViewStateException: Invalid viewstate.
	Client IP: 72.81.21.124
	Port: 50536
	User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET 
CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30)
	ViewState: 
/wEPDwULLTE4MzE4MzkwNDgPZBYCAgMPZBYSAgEPDxYCHgRUZXh0BSVDb21wbGV4IENhc2UgSGlnaGxpZ2h0IChJdGVtcyAx4oCTMTApZGQCBA8PFgIfAAW7A0EgMzUteWVhci1vbGQgQWZyaWNhbi1BbWVyaWNhbiBtYW4gcHJlc2VudHMgdG8geW91IGZvciBoaXMgYW5udWFsIOKAnHBoeXNpY2FsIGV4YW0u4oCdIEhlIGhhcyBubyBzaWduaWZpY2FudCBjb21wbGFpbnRzIGJ1dCBpcyBjb25jZXJuZWQgYmVjYXVzZSBoaXMgb2xkZXIgc2lzdGVyIHdhcyBqdXN0IGRpYWdub3NlZCB3aXRoIHR5cGUgMiBkaWFiZXRlcy4gSGlzIGZhdGhlciBhbHNvIGhhZCB0eXBlIDIgZGlhYmV0ZXMgYW5kIGRpZWQgYXQgYWdlIDU0IG9mIGEgbXlvY2FyZGlhbCBpbmZhcmN0aW9uLiBIZSBoYXMgdHdvIHNvbnMgYWdlIDEwIGFuZCAxMiwgYm90aCA+MTIwJSBvZiBpZGVhbCB3ZWlnaHQgZm9yIHRoZWlyIGhlaWdodC4gSGUgaXMgNuKAmTDigJ0gYW5kIHdlaWdocyAyMTAgbGJzIChCTUkgMjcga2cvbTIpOyBibG9vZCBwcmVzc3VyZSBpcyAxMzgvODggbW0gSGcuZGQCBw8PFgIfAAU0Q3VycmVudCBsYWIgcmVzdWx0cyBmb3IgdGhpcyBwYXRpZW50IGFyZSBhcyBmb2xsb3dzOmRkAgoPDxYIHghJbWFnZVVybAUSaW1hZ2VzL01...]

[HttpException (0x80004005): Validation of viewstate MAC failed. If this 
application is hosted by a Web Farm or cluster, ensure that <machineKey> 
configuration specifies the same validationKey and validation algorithm. 
AutoGenerate cannot be used in a cluster.]
   System.Web.UI.ViewStateException.ThrowError(Exception inner, String 
persistedState, String errorPageMessage, Boolean macValidationError) +116
   System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) +251
   System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter.Deserialize(String 
serializedState) +4
   System.Web.UI.Util.DeserializeWithAssert(IStateFormatter formatter, 
String serializedState) +37
   System.Web.UI.HiddenFieldPageStatePersister.Load() +220
   System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +83
   System.Web.UI.Page.LoadAllState() +35
   System.Web.UI.Page.ProcessRequestMain(Boolean 
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +6953
   System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, 
Boolean includeStagesAfterAsyncPoint) +154
   System.Web.UI.Page.ProcessRequest() +86
   System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context) +18
   System.Web.UI.Page.ProcessRequest(HttpContext context) +49
   ASP.default_aspx.ProcessRequest(HttpContext context) +29
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() 
+154
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& 
completedSynchronously) +64



--------------------------------------------------------------------------------
Version Information: Microsoft .NET Framework Version:2.0.50727.42; ASP.NET 
Version:2.0.50727.210


I have no idea why this happens, and am unfamiliar with viewstate MAC. Can 
anyone give me a starting point? Thanks.
-- 
Nathan Sokalski
njsokalski@hotmail.com
http://www.nathansokalski.com/

One chance is that the application is shut down due to no activity, which 
would make it regenerate the machine keys (in case you haven't specified 
them in web.config) and when keys have changed validating viewstate etc 
cannot succeed.


-- 
Teemu Keiski
AspInsider, ASP.NET MVP
http://blogs.aspadvice.com/joteke
http://teemukeiski.net



"Nathan Sokalski"  wrote in message 
news:O2Zd1180HHA.4236@TK2MSFTNGP06.phx.gbl...

> When I click after about 15 minutes on a page I wrote I recieve the 
> following error:
>
> Server Error in '/' Application.
> --------------------------------------------------------------------------------
>
> Validation of viewstate MAC failed. If this application is hosted by a Web 
> Farm or cluster, ensure that <machineKey> configuration specifies the same 
> validationKey and validation algorithm. AutoGenerate cannot be used in a 
> cluster.
> Description: An unhandled exception occurred during the execution of the 
> current web request. Please review the stack trace for more information 
> about the error and where it originated in the code.
>
> Exception Details: System.Web.HttpException: Validation of viewstate MAC 
> failed. If this application is hosted by a Web Farm or cluster, ensure 
> that <machineKey> configuration specifies the same validationKey and 
> validation algorithm. AutoGenerate cannot be used in a cluster.
>
> Source Error:
>
>      The source code that generated this unhandled exception can only be 
> shown when compiled in debug mode. To enable this, please follow one of 
> the below steps, then request the URL:
>
>      1. Add a "Debug=true" directive at the top of the file that generated 
> the error. Example:
>
>        <%@ Page Language="C#" Debug="true" %>
>
>      or:
>
>      2) Add the following section to the configuration file of your 
> application:
>
>      <configuration>
>         <system.web>
>             <compilation debug="true"/>
>         </system.web>
>      </configuration>
>
>      Note that this second technique will cause all files within a given 
> application to be compiled in debug mode. The first technique will cause 
> only that particular file to be compiled in debug mode.
>
>      Important: Running applications in debug mode does incur a 
> memory/performance overhead. You should make sure that an application has 
> debugging disabled before deploying into production scenario.
>
> Stack Trace:
>
> [HttpException (0x80004005): Unable to validate data.]
>   System.Web.Configuration.MachineKeySection.GetDecodedData(Byte[] buf, 
> Byte[] modifier, Int32 start, Int32 length, Int32& dataLength) +2549692
>   System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) +214
>
> [ViewStateException: Invalid viewstate.
> Client IP: 72.81.21.124
> Port: 50536
> User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET 
> CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30)
> ViewState: 
> 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...]
>
> [HttpException (0x80004005): Validation of viewstate MAC failed. If this 
> application is hosted by a Web Farm or cluster, ensure that <machineKey> 
> configuration specifies the same validationKey and validation algorithm. 
> AutoGenerate cannot be used in a cluster.]
>   System.Web.UI.ViewStateException.ThrowError(Exception inner, String 
> persistedState, String errorPageMessage, Boolean macValidationError) +116
>   System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) +251
> 
> System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter.Deserialize(String 
> serializedState) +4
>   System.Web.UI.Util.DeserializeWithAssert(IStateFormatter formatter, 
> String serializedState) +37
>   System.Web.UI.HiddenFieldPageStatePersister.Load() +220
>   System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +83
>   System.Web.UI.Page.LoadAllState() +35
>   System.Web.UI.Page.ProcessRequestMain(Boolean 
> includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +6953
>   System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, 
> Boolean includeStagesAfterAsyncPoint) +154
>   System.Web.UI.Page.ProcessRequest() +86
>   System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context) +18
>   System.Web.UI.Page.ProcessRequest(HttpContext context) +49
>   ASP.default_aspx.ProcessRequest(HttpContext context) +29
> 
> System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() 
> +154
>   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& 
> completedSynchronously) +64
>
>
>
> --------------------------------------------------------------------------------
> Version Information: Microsoft .NET Framework Version:2.0.50727.42; 
> ASP.NET Version:2.0.50727.210
>
>
> I have no idea why this happens, and am unfamiliar with viewstate MAC. Can 
> anyone give me a starting point? Thanks.
> -- 
> Nathan Sokalski
> njsokalski@hotmail.com
> http://www.nathansokalski.com/
>