I just went through that.

On your Linux box you can:

*       convert the ext3 filesystems back to ext2, or

*       Upgrade to the 4.2.1 Linux client and convert the ext3 filesystems
to REiserfs, or

*       Upgrade to the 4.2.1 Linux client and add to your dsm.sys file:

                VIRTUALMOUNTPOINT "/"
                VIRTUALMOUNTPOINT "/boot"
                etc. for all other ext3 filesystems

                When you do this the filesystems still won't show up in the
backup GUI, but they
                WILL back up via the scheduler or the command line, and they
show up OK
                in the restore GUI window.