Upgrade from RHEL 4.6 to 5.1 errors

[Chris Henderson]

I have upgraded Red Hat Enterprise Linux AS release 4 (Nahant Update
6) to Red Hat Enterprise Linux Server release 5.1 (Tikanga) - the
system starts without any problem but while booting up I get "errors":
"momery for crash kernel (0x0 to 0x0) notwithin permissible range."

I also get lots of error from udevd (I couldn't capture all the errors
& they don't seem to be in any log file): "udevd: add_to_rules:
invalid kernel operations"

udevd seems to be running (/sbin/udevd -d).

Why these errors are happening and how can I get rid of them?

Thanks.