Login error -"Path to long"

One possible solution is the following. (if that was really the only change)

Log on as the local Administrator and verify that either the user or a group (of which the user is a member) has at least read access to the root of the system drive. To accomplish this if the desktop is blank, follow the procedure below:

Start Task Manager by pressing CTRL+ALT+DELETE .

On the File menu, click New Task .

In the Run dialog box, start Explorer.exe or Winfile.exe .

View the security permissions of the system drive.

If the user or group does not have this access, add it to the directory permissions for the user or group. Do not select the Apply To Subdirectories check box.

For additional information, please see the following article in the Microsoft Knowledge Base:
ARTICLE-ID: Q148437
TITLE : Default NTFS Permissions in Windows NT

MORE INFORMATION
If a user logs on to a workstation (either locally or to a domain) and is not listed by group or nameto have any access permissions to the root directory where the system files reside, the following problems can occur:

If the user logs on to the domain from the workstation or member server, he or she will get a dialog box with the following error, followed by a blank desktop:
Can't access this folder. The path is too long.
However, a profile is created in the %SystemRoot%\Profiles directory for that user.

If the workstation or server is not a member of a domain, or if the user decides to log on locally, the error message may or may not be displayed, but a blank desktop with the profile created in the profiles directory will occur.

there are some more instances that I have found on the MS KB, (passing the limit of maxpath, if this answer doesn't help search on the MS KB using the "path is too long" string,

regards,

I've seen this before, it had to do with permissions being changed on the root directory.

You may want to check them by logging on as the local admin... (if you get the same message followed by a blank screen, hit Ctrl, Alt Delete to start the task manager. Under File, click New Task. In the Run dialog, start Explorer.exe and check the permissions on the system drive.)
In my case, they were changed... That's the only time I've seen this particular message... hope it helps!

Do you have error messages?, like :
??? Path too long
??? Error cannot delete file: cannot read from source file or disk
??? Cannot delete file: Access is denied
??? There has been a sharing violation.
??? Cannot delete file or folder The file name you specified is not valid or too long. Specify a different file name.
??? The source or destination file may be in use.
??? The file is in use by another program or user.
??? Error Deleting File or Folder
??? Make sure the disk is not full or write-protected and that the file is not currently in use.
??? Error Copying File or Folder.
??? Cannot remove folder.
??? The filename or extension is too long.
??? Path too deep.
??? Destination Path Too Long.
??? Could not find this item.
??? Filename is not valid.
??? The file could not be accessed.
??? The path you entered, is too long. Enter a shorter path.
??? File Name could not be found. Check the spelling of the filename, and verify that the file location is correct.

LONG PATH Tool 3.6 at http://LongPathTool.com