99% of the time this is due to circular logging still enabled on your Exchange Stores. Check it is disabled and restart the information store service.
You need to check the detailed backup report, which can only be viewed on the client side console. Open the DataBunker console > Hover of Reports > Click Backups Reports > Click on the schedule name in question > Expand the latest report by clicking the double arrow icon on the left side. If you scroll down the report and look at the “Result Messages” it will explain the exact cause of the problem. Most of the time the information provided is self-explanatory on how you can fix the problem, but if you need any assistance please let us know.