APEX

Every now and then, usually toward the end of the day, I'll be working in the development tool and suddenly get thrown out to an Apex login screen. It doesn't seem to be related to "what" I'm doing at the time. It's happened most frequently when I've just pressed the 'apply changes' button. Today, I had backed up to the page selection screen and selected a page when - BOOM! There are no visible errors.

Any ideas as to what might be happening?
Are there error logs somewhere?

I'm on 3.2.0.00.27 and very new to Apex.

Any help is much appreciated.

Thanks,
Lothar