If DA could put in the session.c file from the .9 version, or/and add whatever should be done to the Apache config to have PHP use the correct session directories, then we should be able to simply run the ./build update and ./build php and/or ./build apache to upgrade our boxes, not to have the error occur again.
I don't trust myself to do this, and recompile PHP on my own. So if DA could do it, it would be excellent. Else, we would have to wait for a PHP 4.3.10rev.
This has been an old PHP problem, but as you can see from the bug-report on PHP.net, half of the filings have been from the last two days - a lot of people are having trouble with this, and it looks like a serious bug. Should be fixed urgently!