System State Backups using NTbackup fail with error 0x800423f4 (relating to volume shadow copy)

We have a Windows Server 2003 R2 running Service Pack 2. It is a domain controller (Global Catalog) and our main internal DNS server. We run a System State backup of the machine to back up Active Directory information and save the backup to a different server.

This server has a single drive (C:), and we do have Shadow Copies enabled for the volume (which are completing successfully).

The System State Backup is now failing with the following listed in the backup logs:

Volume shadow copy creation: Attempt
1. "Event Log Writer" has reported an error 0x800423f4. This is part of
System State. The backup cannot
continue.

Error returned while creating the
volume shadow copy:800423f4 Aborting
Backup.

---

The operation did not successfully
complete.

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When doing a vssadmin list writers, we sometimes get the following reported for the Event Log Writer (other times it says that it is in the state of "[1] Stable" with "No error"):

Writer name: 'Event Log Writer' Writer Id:
{eee8c692-67ed-4250-8d86-390603070d00}
Writer Instance Id:
{c7194e96-868a-49e5-ba99-89b61977753c}
State: [8] Failed Last error:
Retryable error

We have tried disabling the event log service via the registry, rebooting, deleting the event log files from the drive, then re-enabling the service via the registry and rebooting, but this didn't seem to solve the issue.

We also get an error message when in the event viewer when trying to open the log for the "File Replication Service" of "Unable to complete the operation on 'File Replication Service'. The security descriptor structure is invalid."

I have searched the error via Google and tried a number of different things, but nothing has seemed to help.

Any suggestions on what we might try to get the Event Log Writer to behave would be greatly appreciated!