This event may also be symptomatic to other problems. I recently used Acronis MigrateEasy to move the C: partition of a W2K domain controller from my small and elderly hard drive onto a larger faster hard drive. The disk image and migration went very smoothly, so I did not have any immediate evidence that anything was amiss until I began receiving a number of these events, along with EventID 1000 from source Userenv. Further, I could no longer force replication between the migrated DC and its "partner" DC, although both DCs were shown in the AD sites section of the MMC.
In order to clear up the problem, I had to demote the migrated DC to a member server, clean up the metadata on the replication partner, then promote the migrated DC and restore the replication links. The entire process is documented within TechNet Active Directory Operations Guide, Appendix B. After about 24 hours, all error messages tapered off and disappeared.
Apparently, this problem occurs if FRS failed to access a domain controller within a File Replication polling interval (5 min by default). The reason for this could be a domain controller becoming unreachable, network problems, etc.. Microsoft suggests that the File Replication Service should be restarted. See ME253859
for more details.