Backup completing with exception

Hi

whenever i am doing complete or differential backup on backup exec 2012, it  ejects the rdx tape at 100% and status still displaying backing up. When i put back the tape the job stops and says completed with exception.

i am told vss is not working. i can not also do the system backup either. below is the error message:

The backup options or selections for this job have changed since the last time it ran. You should run the full backup instance of this backup definition as soon as possible to ensure complete protection.
 

Backup- Foods-AD.foods.localdomain
- Snapshot Technology: Initialization failure on: "\\Foods-AD.foods.localdomain\D:". Snapshot technology used: Microsoft Volume Shadow Copy Service (VSS).
V-79-10000-11226 - VSS Snapshot error. The Microsoft Volume Shadow Copy Service (VSS) snapshot technology selected returned: "Unexpected provider error". Ensure that all provider services are enabled and can be started. Check the Windows Event Viewer for details. 

What shall be done?

I checked the vss service and it is operating.