Comodo Backup error 33

Hi there

I tried to do a backup with the latest Beta version(It just automatically installs ) and I get the following error.
25.05.2014 15:54:42 Disk driver not available.
25.05.2014 15:54:42 The source partition(s) will be locked during backup.
25.05.2014 15:54:42 Creating new backup…
25.05.2014 15:54:42 Deduplication is disabled because compression level is not highest.
25.05.2014 15:54:42 Creating full backup “F:\Backups\Comodo\Comodo Backup\Disk_1_inc_disk.cbu”
25.05.2014 15:54:42 Initiating backup operation…
25.05.2014 15:54:42 Gathering information…
25.05.2014 15:54:42 Cannot lock one of the volumes(C:) that is being backed up.
25.05.2014 15:54:42 Please close any programs that might be using it and try again.
25.05.2014 15:54:42 Otherwise the backup operation cannot be performed.
25.05.2014 15:54:43 Backup failed with code 33 (Invalid request).

If anyone can please assist.

regards
M. Ajam