Consult the administrator of the Exchange server to rectify the problem. Please ensure that Exchange circular logging is ...

1. Consult the administrator of the Exchange server to rectify the problem. Please ensure that Exchange circular logging is turned off. Synchronization jobs may continue to fail until this issue is resolved.
2. Last backup might have failed after log truncation. 

In the Protection task area, click 'Create recovery point' and select 'Full backup' option.
3. If the protected datasource is an Exchange 2010 database, make sure that multiple copies of the database are not protected for FULL backup. DPM supports protecting only one copy of the database using FULL backup and the other copies have to be protected using COPY backup.