A problem may occur when you run a backup - it fails and for each database, you see a message that looks like this:
Object SharePoint_Config failed in event OnBackup. For more information, see the spbackup.log or sprestore.log file located in the backup directory.
SqlException: A system assertion check has failed. Check the SQL Server error log for details. Typically, an assertion failure is caused by a software bug or data corruption. To check for database corruption, consider running DBCC CHECKDB. If you agreed to send dumps to Microsoft during setup, a mini dump will be sent to Microsoft. An update might be available from Microsoft in the latest Service Pack or in a QFE from Technical Support.
BACKUP DATABASE is terminating abnormally.
Wow - pretty scary eh? Most likely if you check your Health monitor, you see another error:
Expired sessions are not being deleted from the ASP.NET Session State database.
DON'T PANIC - It turns out to be a simple problem! The SQL Server Agent Service is NOT running. Thus the backup cannot get proper control of the database and the timer job to clear session state won't be running.
Start the Agent on SQL Server first then for the Backup issue:
Delete whatever backup files were created (they are junk), start the backup again.
For the Health error:
Open the Health Monitor from Central Admin, click on the error (Expired sessions...) and click the Re-analyze button.