Hi,
kernel version with asterisk dahdi are sometimes a p** in the a**
Asterisk current 1.8 requires kernel <= 2.6.18-308.16.1.el5, but SME8 is already beyond that, breaking compatibility with digium and asterisk rpm's.
I've created a little script here:
http://wiki.contribs.org/SME8_stick_to_kernel_version