"System.Web.HttpException: Unable to validate data" error

[Fresno Bob]

I get the following very intermittant error.
System.Web.HttpException: Unable to validate data. at
System.Web.Configuration.MachineKeySection.GetDecodedData

The form encoding type is for uploading files (the multipart one). Is this a
similar error the ViewState validation "bug" where the page throws an error
if you naviagate too quickly and don't give the page enough time to load in
the encrypted viewstate?

Regards, Chris.