Ghost 14 cannot dismount drive

I had backup jobs setup with Norton Ghost 14 and it was working fine for months, then started failing. I decided to do a full copy drive backup manually and got the following error:

 

This operation cannot be performed while the destination is in use.

Close any applications that may be using the destination drive and select 'Retry'.

Or, select 'Ignore' to force a dismout of the drive and continue the operation.

 

I tried to close all background apps but with no luck. I am using Windows Vista 64bit. Is there something I have to do to dismount my drive?