512 MB of space is the standard initial allotment on Lotus; see the
Country Restrictions thread for more info (and how to get upgraded if need be).
The "disk full" error is for the server as a whole, not your account in particular. It happens from time to time both because of the activity of other users on the server and because of server logs/error logs, etc. It usually just takes a little bit of time to clean out the system, delete old files/accounts, et cetera, but sometimes it can take a while to track user code that's writing a lot of log information. Please be patient in the meantime.