Unable to Eject USB HDD

We recently found that on a server the USB Hard-disk used for backups could not be ejected and therefore safely removed.  This behaviour only started after AVG was installed. 

Bizzarley when using Process Monitor to see what program was accessing the disk it was showing wbengine.exe and vds.exe which are both to do with Microsoft Backup.  The backup was however reportedly working correctly and finished hours prior.

We went on a wild goose chase looking into why the backup process was continually running, only to find a clue in the Event Log:

The application \Device\HarddiskVolume2\Program Files (x86)\AVG\AVG9\avgchsva.exe with process id 496 stopped the removal or ejection for the device USB\VID_0930&PID_0B1A\20111130220195.

Searching for information about this resulted in the following forum post at AVG:
http://forums.avg.com/gb-en/avg-forums?sec=thread&act=show&id=33311

 So it would appear that the solution is to turn the cache off, at least until AVG respond with a fix, which given that this post is from 2009, I assume the fix is not coming.

So disable the cache in this way:
- Open AVG user interface and Advanced settings.

- In left branch select "Cache Server".

- Uncheck "Caching enabled" and save settings by OK.