Alright. If you ever come into the same situation I was in and need a newer kernel (2.6.32 or up, perhaps also 2.6.31) on some system with old iptables package (versions below 1.4.0 I think, 1.3.5 in my case: CentOS5/RHEL5), you might get this helpful error message when using the iprange module in your iptables rules:
iptables: Unknown error 18446744073709551615
Or even more helpful, if you use iptables-restore to load your rules, you will get an error in the line containing the COMMIT statement (
iptables-restore: line X failed).
The reason for this is that the netfilter guys have removed an interface to the iprange module in kernel version 2.6.31 or 2.6.32 (see my bug report at #711 of the netfilter bugzilla).
Just posting this so it might hopefully help others if they get into the same situation.