space problem

Hi,
Our Postgresql server (version info in the end of message) has been
running well in light test use, except yesterday appeared strange
problem. I could not any more create table, sequence, database or
anything. Psql just said: ERROR: Cannot create ...
When I tried "createdb" it said that "No sapce enough in device".
Then we droppped one database (from two! we have created) and after
that creating was again possible. But all the time there was space in
the disks. df said:
Filesystem            Size  Used Avail Use% Mounted on
/dev/hda1             801M  327M  434M  43% /
/dev/hdb1             537M  274M  236M  54% /usr
and it did not much change during drop database. The databases are
practically empty!
According to linuxconf there shoud not be any disk quotas.

So what could be going on?
I would like get this clearer before we switch to production use!

Thanks
Esa Pikkarainen

Versions:
 - PostgreSQL 7.0.2 on i686-pc-linux-gnu, compiled by gcc 2.95.3
 - Linux (Mandrake) version 2.2.15-4mdk
   (chmou@kenobi.mandrakesoft.com) (gcc version 2.95.3 19 991030
   (prerelease)) #1 Wed May 10 15:31:30 CEST 2000