Thanks for checking those things! If it crashed when the lister was closed then we can rule out the toolbars etc.
It's interesting that the crash didn't happen with the tree closed, but that may just have been luck as without a lister there would not be a tree either.
Could you see if any crash dumps were created at the time of any of the crashes, and if so zip them up and send them to me via a private message?
Another file which may help diagnose the problem is recent.osd which you can find by typing /dopuslocaldata into a lister, then going into the State Data folder below where it takes you.
Many thanks for your time helping us track this down.