All of a sudden, and for no apparent reason, Webmin is crashing. I cannot figure out why.

The server is an Ubuntu 10.04.03.LTS .. everything else seems to be working on it. I re-start Webmin, which goes fine. Then I once again go into Virtualmin, click on a server, and I get a connection refused. ps ax reveals no Webmin. So I re-start it, and I can walk around fine in its menus, etc. Click on a virtual server, and it's gone again.