There is a bug in the Xsession script shipped with RHEL 5. A "umask" command was accidentally spelled as "unask". This causes Xsession errors to be redirected to /tmp/xses-$USER-XXXXXX instead of $HOME/.xsession-errors, but it otherwise harmless as far as I can tell.
This request was evaluated by Red Hat Product Management for inclusion, but this component is not scheduled to be updated in the current Red Hat Enterprise Linux release. This request will be reviewed for a future Red Hat Enterprise Linux release.
*** This bug has been marked as a duplicate of 239471 ***
239471 has nothing to do with this bug, I think you mean 239478 (because that's what 236629 refers to), but I'm not allowed to access that.