I recently moved our 5.01.02 installation from our DEV to PROD server.  Everything works wonderfully except the login. 

I can login no problem while on the local server.  However, if I am on another machine, once I click Submit from the Login module, I am shown a non-descript error page ("An error has occured.") and can never successfully log in to the application.  When I look at the logs, I get a "Failed to load view_state.  The control tree into which view_state is being loaded must match the control tree that was used to save view_state during the previous request." error as well as "The process cannot access the file
'E:\DotNetNuke\Portals\_default\Cache\180564D7100F5C64B401E53D1AB057D4.resources' because it is being used by another process."

I have cleared the cache, restarted the app, tested from other machines and still no luck.  Any ideas?

Thanks for the reply.  There doesn't seem to be any reasoning behind which computers are able to successfully log on and those that are not.  From my work laptop, a co-worker's laptop, and another virtual machine on our network, the logins fail.  I've tried with both IE and Firefox.  From another server in our DMZ, my iPhone, and my home laptop and desktop, the logins are successful.

When you say it could be the network process permissions, are you referring to the NETWORK SERVICE account?  That ID has the proper level of access to the app folder as far as I can tell.

When I moved the app from DEV (where this problem does not exist), I simply copied the directory to PROD, replaced the server names, and duplicated the folder permissions.  I restored the SQL Server from backup over the previous PROD db.  The only difference I know of between the two environments is PROD has a separate server for the database, DEV runs everything off the same box.

Any more ideas out there?  :)

I'm still experiencing this problem.  It's only occurring on machines on our domain - machines outside of the domain can log in without issue.  Any ideas out there??