Error: Unable to validate data.WHY?

[Guest]

Dear I have the following problem:

Message:
Unable to validate data.

Trace:
at System.Web.Configuration.MachineKey.GetDecodedData(Byte[] buf, Byte[]
modifier, Int32 start, Int32 length, Int32& dataLength) at
System.Web.UI.LosFormatter.Deserialize(String input)

the portal is running months ago and this is the first time this error
generated, why this happening?

 

[Axel Dahmen]

I don't know, but perhaps the ViewState string has become too big? I'd check
if there are some server-side controls which do not necessarily need
EnableViewState=True.

HTH,
Axel Dahmen