This has been happening to me ( am I the only person running IceWm?) ever since Natty was in Alpha. I installed Icewm- picking it from the GDM menu results in an almost immediate return to GDM. I assume it is crashing. IF I run icewm itself from GDM by installing a modified desktop file, it's fine, but then I miss out on several icewm features, like running a startup file. I have asked several places and did Google searches but they don't turn up anything. I have reinstalled IceWm several times. Natty is the only dist this happens on...I also run Maverick and Debian Sid on other partitions.