This occurs when the log sequence of MS Exchange was altered by other backup software, e.g. NTBackup. Thus when the Backup Manager next performs a MS Exchange backup, the Exchange log sequence would not match the one that it is expecting. With the broken sequence, the Exchange server cannot be restored to its latest state.

To resolve this problem, you need to deactivate all other backup software that is operating on MS Exchange, and then you need to perform a Full MS Exchange database backup manually via the Backup Manager.

Alternatively, instead of backing up transaction logs during the weekdays, you can consider doing Full Exchange Database backup on a daily basis with the In-File Delta option enabled. This should avoid interference from other backup software while keeping the amount of upload data to minimal.