Invalid viewstate

[Oscar Thornell]

Hi,

I have encountered a problem in our dev.test environment (W2003/ASP.NET
2.0). All of a sudden one of our asp.net web applications has seized to
function.
- We have not changed the code for this particular application for months
- We have not re-configured the IIS or the OS in anyway for months

All of a sudden every request in this application throws an exception
stating that the Viewstate is invalid.
- This is an isolated machine (i.e not a cluster)
- No load is put on the machine so the processes should have to recycle
frequently

The application runs fine in other similiar envrionments (dev.stage,
acceptance, production).

My questions:

Does anyone know if an Invalid Viewstate has been caused based upon the
requesting clients UserAgent?

Does anyone know if MS has released a security update or similiar that could
cause this problem (the effected machine is the only one that recives auto
updates..)?

The machineKey is set to Autogenerate...ASPNET is running under
Network_Service could that account update the registry hive??

Regards
/Oscar