'Cannot Load User Profile' but profile is NOT corrupt!

OK, I know this topic has appeared before, but please take a look. Previous
solutions I have found don't seem to apply here.

We have 15 workstations running Windows XP Pro on a domain with Windows 2003
Server and Active Directory. No roaming profiles, just a home directory (My
Documents) mapped to the server.

Frequently, users try to log on to a system but receive the 'Cannot Load
User Profile' error message (see below for exact event descriptions). It
seems that ntuser.dat cannot be accessed because it is being used by another
process. I don't believe the profile to be corrupt because a reboot will
solve the issue.

This occurs to several users on several workstations.

Please help if you can! Thanks.

Event Descriptions
1508
Windows was unable to load the registry. This is often caused by
insufficient memory or insufficient security rights.

DETAIL - The process cannot access the file because it is being used by
another process. for C:\Documents and Settings\kgooch\ntuser.dat

1502
Windows cannot load the locally stored profile. Possible causes of this
error include insufficient security rights or a corrupt local profile. If
this problem persists, contact your network administrator.

DETAIL - The process cannot access the file because it is being used by
another process.

1515
Windows has backed up this user's profile. Windows will automatically try to
use the backed up profile the next time this user logs on.

1511
Windows cannot find the local profile and is logging you on with a temporary
profile. Changes you make to this profile will be lost when you log off.