Ghost 15 - Cannot Delete Old Backup Files (Symantec Image File)

I'm trying to manually delete old Ghost 15 backup files (Symantec Image File), but half way through the delete it says 'the file is being used by another program, please close down that program', but there is nothing to close down.

 

I have uninstalled Norton Ghost 15 from my computer and tried but it says the same.

 

Would appreciate any help.

 

Thanks

Richard