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ViewState validation error ASP.NET

royend asked
Last Modified: 2013-11-07
Dear experts,
Until yesterday everything was working perfect for my website. Then, my users started reporting about invalid ViewStates:
HttpException (0x80004005): Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.

I googled and found a method which would set the ViewState constant, and thus securing that the ViewState would be correct for all users. This, however, made the ViewState not unique for my users, as it seems they share the same session-data. Sharing session-data resulted in frequently "Object does not exist" when a user tried to load some session-variable.

I guess the only correct thing would be to go back and try to fix the first error: The error of ViewState validation for my users.

Does any of you have any solution to this problem?
Or a hint about what may be wrong?

Looking forward to your help :)
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