Veritas fails to back up a log but Informix thinks it did

I'm using Veritas Netbackup for Informix along with Informix Onbar to perform backups. Occasionally I see error messages in the Veritas logs that are not consistent with the messages appearing in the Informix online log. For the Veritas report: machine: /instance/4/18254 level=Default-Policy, 0 KB 00:11:12 1 files Error: media position error (86) From the online log: 13:36:41 Logical Log 18254 Complete. 13:36:52 Logical Log 18253 - Backup Completed 13:36:52 Logical Log 18254 - Backup Started 13:37:06 Logical Log 18254 - Backup Completed onstat -l output: onstat -l | grep 18254 b959c10 77 U-B---- 18254 50d131 750 750 100.00 So it appears that Informix thinks the log got backed up, but Veritas is telling me it didn't get backed up. When I use the Veritas xbp tool to look at what has been backed up, the log 18254 is not there. How do I get Informix to attempt the backup again? Many thanks... Mike