|OK, I found the issue causing the 6145 errors.
Was doing some more troubleshooting this AM, and came across a Warning. This warning was propagating at the same 5 minute intervals as the 6145 errors:
Log Name: Application
Date: 8/31/2010 8:37:54 AM
Event ID: 1202
Task Category: None
Security policies were propagated with warning. 0x534 : No mapping between account names and security IDs was done.
Advanced help for this problem is available on http://support.microsoft.com. Query for "troubleshooting 1202 events".
Error 0x534 occurs when a user account in one or more Group Policy objects (GPOs) could not be resolved to a SID. This error is possibly caused by a mistyped or deleted user account referenced in either the User Rights or Restricted Groups branch of a GPO. To resolve this event, contact an administrator in the domain to perform the following actions:
1. Identify accounts that could not be resolved to a SID:
From the command prompt, type: FIND /I "Cannot find" %SYSTEMROOT%\Security\Logs\winlogon.log
The string following "Cannot find" in the FIND output identifies the problem account names.
Example: Cannot find JohnDough.
In this case, the SID for username "JohnDough" could not be determined. This most likely occurs because the account was deleted, renamed, or is spelled differently (e.g. "JohnDoe").
2. Use RSoP to identify the specific User Rights, Restricted Groups, and Source GPOs that contain the problem accounts:
a. Start -> Run -> RSoP.msc
b. Review the results for Computer Configuration\Windows Settings\Security Settings\Local Policies\User Rights Assignment and Computer Configuration\Windows Settings\Security Settings\Local Policies\Restricted Groups for any errors flagged with a red X.
c. For any User Right or Restricted Group marked with a red X, the corresponding GPO that contains the problem policy setting is listed under the column entitled "Source GPO". Note the specific User Rights, Restricted Groups and containing Source GPOs that are generating errors.
3. Remove unresolved accounts from Group Policy
a. Start -> Run -> MMC.EXE
b. From the File menu select "Add/Remove Snap-in..."
c. From the "Add/Remove Snap-in" dialog box select "Add..."
d. In the "Add Standalone Snap-in" dialog box select "Group Policy" and click "Add"
e. In the "Select Group Policy Object" dialog box click the "Browse" button.
f. On the "Browse for a Group Policy Object" dialog box choose the "All" tab
g. For each source GPO identified in step 2, correct the specific User Rights or Restricted Groups that were flagged with a red X in step 2. These User Rights or Restricted Groups can be corrected by removing or correcting any references to the problem accounts that were identified in step 1.
Fortunately, it was embedded with troubleshooting instructions.
Our "Guest" account is renamed. When I was adding users to the Security Settings>Local Policies>User Rights Assignments>Deny log on through Remote Desktop Services, I misspelled the renamed "Guest" account name. Removed the misspelled name, then "browsed" for the correct account, and the errors stopped.
Also, I found "Error 1332" in the winlogon.log file:
Error 1332: No mapping between account names and security IDs was done.
Cannot find "misspelled account".