backup exec 2010 r2

Hello

Backups have been failing for past 2 weeks with the folliwng error

Error             : e0001904 - A failure occurred querying the Writer status.  Writer Name: Exchange Server, Writer ID: {76FE1AC4-15F7-4BCD-987E-8E1ACB462FB7}, Last error: The VSS Writer failed, but the operation can be retried (0x800423f3), State: Failed during prepare snapshot operat
For additional information regarding this error refer to link V-79-57344-6404

Have looked at various solutions but nothing have resolved this. Registerd VSS files, reboot of server, Resrat of Exchange services.

Any suggestions appreciated.

Thank you