Mounting sunsite.doc.ic.ac.uk using the advertised method of using the IP 193.63.255.4 used to work fine with Redhat 6.1. With 6.2 the mount attempt hangs. Downgrading to the 6.2 RPM of mount cures the problem again, though it logs "Mount older than kernel" in the syslogs.
This looks similar to what I reported in 10647. I had to downgrade to mount-2.9u-4.i386.rpm to get it to work the NFS. Perhaps you could double-check the obvious (make sure portmap is running) and post a copy of what /var/log/messages reports when mount fails. Oh, and please mention the exact names of the RPMs that work or don't work so there's no confusion.
Need I say - portmap was running. Yes, I downgraded to mount-2.9u-4 just as you did. Can't remember what appeared in the logs for a mount failure, and I'm afraid it is impractical for me to check: this is my production server.
*** This bug has been marked as a duplicate of 10647 ***