I am having the same problem here - when I attempt to perform a backup to workstation, I get a blank page and nothing else.
I'm currently using SME6.0b2 and attempting to backup to an XP home edition machine. The SME server itself is running a RAID5 array, but I like to make a backup of the server prior to installing any updates or contribs.
Simply reporting this as a bug will not assist either Samer or myself, as for me, this is my primary means of backing up my server. The two of us have this problem, does anybody else - and, more importantly, - has anybody found a fix for this??