xfce4-session manager crashes when loaded while already running AND session management is set to automatically save session on log out. xfce4 would start up after being closed, open 2 rxvt shells (i had them open when it crashed) then crash back to the console. I deleted the contents of ~/.xfce4/session/ and was able to start x and turn off the switch to save session on log out, after which it was stable again.
Additional information: I am running gentoo ~x86, where xfce4-session is blocked. I had downloaded the latest cvs build of xfce4-session and compiled and installed it. While I was sending an email to the maintainer of the program at gentoo, I realized I didn't know the version of the program and tried to run "xfce4-session -v", on the off chance that might give me a version number... oops. I sent off the email, and tried to close the extra session manager, which caused x to close. When I restarted xfce4, the process given in the description field occurred.
I committed a fix to CVS HEAD. xfce4-session now checks for an already running session manager prior to starting up. Thanks for the report.
This was fixed in CVS and a tarball test version was also released.