Why does this happen?  How to fix it?

Once in a while I get error in ~/ScriptResource.axd?d=...

System.Reflection.TargetInvocationException: Exception has been thrown by 
the target of an invocation. ---> 
System.Security.Cryptography.CryptographicException: Padding is invalid and 
cannot be removed.

   at 
System.Security.Cryptography.RijndaelManagedTransform.DecryptData(Byte[] 
inputBuffer, Int32 inputOffset, Int32 inputCount, Byte[]& outputBuffer, 
Int32 outputOffset, PaddingMode paddingMode, Boolean fLast)

   at 
System.Security.Cryptography.RijndaelManagedTransform.TransformFinalBlock(Byte[] 
inputBuffer, Int32 inputOffset, Int32 inputCount)

   at System.Security.Cryptography.CryptoStream.FlushFinalBlock()

   at 
System.Web.Configuration.MachineKeySection.EncryptOrDecryptData(Boolean 
fEncrypt, Byte[] buf, Byte[] modifier, Int32 start, Int32 length, Boolean 
useValidationSymAlgo)

   at System.Web.UI.Page.DecryptString(String s)

   --- End of inner exception stack trace ---

   at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] 
arguments, SignatureStruct& sig, MethodAttributes methodAttributes, 
RuntimeTypeHandle typeOwner)

   at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] 
arguments, Signature sig, MethodAttributes methodAttributes, 
RuntimeTypeHandle typeOwner)

   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags 
invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean 
skipVisibilityChecks)

   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags 
invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)

   at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)

   at System.Web.Handlers.ScriptResourceHandler.DecryptString(String s)

   at 
System.Web.Handlers.ScriptResourceHandler.DecryptParameter(NameValueCollection 
queryString)

   at System.Web.Handlers.ScriptResourceHandler.ProcessRequest(HttpContext 
context)

   at 
System.Web.Handlers.ScriptResourceHandler.System.Web.IHttpHandler.ProcessRequest(HttpContext 
context)

   at 
System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()

   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& 
completedSynchronously)