We have a server with Windows Server 2008 Standard installed. We added users and user groups in order for other computers to have access to specific shared folders and files. Obviously, we've set some shared folders to be accessed by some users but not others.
It all worked well until some day. I don't know exactly what happened then. Now, the majority of times whenever I try to access one of my shared folders, I get the message You do not have permission to access \\server\foldr, even though I have been given access to the folder, both in the sharing permissions and the NTFS ones.
This happens equally to all the network users. Only the folders marked for access by Everyone can be accessed.
Another curious thing is that when I go to Computer Management\Shared Folders\Sessions on the server, my client computer is enlisted as GUEST, instead of the user's name, although the Guest property is set to No.
I've already tried resetting permissions on the folder, adding new users, changing credentials on the client computer... nothing seems to work. Do you know what seems to be the problem?
Edit: Follow-up to Dmitry's questions:
Security event 552 does not appear on the logs. Instead, I'm getting event 4776 stating that I have logged in with the "Guest" logon account.
Accessing \\server\c$ asks for my credentials, but either they're not accepted or I do not have permissions to access c$. I have experienced this already when trying to map a network drive to \\server\foldr with specific credentials, somehow my credentials are never accepted.
Turning off UAC didn't help.
The clients' PCs have a range of Windows OS's from XP to 7. My PC in particular has Win 7 RC.
2nd Edit: I disabled the Guest account and found out that my client PC's username is different from the username I was trying to use (I really thought that they were equal, but apparently I changed it when I formatted and reinstalled the OS). So now my question is: is there any way that I can access the shared folders while keeping the current usernames on both server and client computers?