Which version exactly of RHEL have you currently got
Code:
cat /etc/*release*
uname -a
There was a recent update to RHEL 5.6 which broke Gnome & Evolution, but the fix has been issued.
http://www.linuxquestions.org/questi...-gnome-875328/
If this is your issue, another yum update should fix it.
My Centos 5.6 had exactly this problem, but it's fine now.