Thanks for your cooperation. Did you test the file manager in an alternative browser, like Firefox?
Yes, at least I tried to use Firefox in the Virtuozzo file manager even though it performed badly in Plesk.
It's the same with the other browsers except I gave up using them in Plesk.
Internet Explorer 7 is the only browser of 5 which is usable in Plesk even though it performes badly, it's also the only browser I could use to access Virtuozzo File manager but just some of the time as it gave errors most of the time.
Update: I forgot to mention that I tried to log me in from a Linux machine too from my home network, it was same.