Hello,
I think I am having the same problem, but don't understand the solution (syncronize ) proposed in the thread. I realize it is due to my lack of experience in .Net application.
I see where the machine key is in web.config. Does this value need to be changed? Possibly to the value in the previously working installation?
Do values in aspnet.applications, membership, users..etc. need to be changed also?
Thank you for your help. Mark