This is against the kernel-2.4.0-0.43.6 package. Some modules no longer exist in 2.4, as they have been merged into other modules or changed name. This report is on this happening with the 3c90x, which is now part of the 3c59x module - when upgrading ,networking no longer works as modules.conf needs to be modified.
This was fixed in RHL 7.1.