session problem

Hello, I've got a problem with sessions. in php on linux with php version 4.0.2 and apache 1.3.12. Php is compiled with the following flags: .--with-interbase=[DIR] --with-apache=[DIR] --enable-track-vars. Generally everything works fine until for some reason I can not retrieve any page from the apache which uses php session. It seems that everything is ok the session file is created in tmp dir., it consists correct data but php is hanging up when I try to the start session. Its strange that I can use pages with the same session few times until php stops. When I remove session file by hand php starts again, of course I'm loosing session context but script processing is continued. I had the same with php4.0.1pl2 and php4.0.2. And two another questions: 1. How to start garbage collector and does it remove past session files? 2. In documentation there is described very briefly how to garbage collection mechanism works (configuration variables gc_probability) but to be honest I didn't understand it fully. Could someone explain it to me in more human form? Thanks in advance.