Why I cannot mount to RH4?

Hi,
I want to mount a rh4 filesystem from a solaris 10 machine. And I has modify the /etc/exports file and restart the nfs process. Everything seems to be right. But when I want to mount it from the solaris(mount -F nfs -o rw radiohead:/export/home /mnt/radiohead), the solaris complains "nfs mount: mount: /mnt/test: Not owner".

So after searching varies sources, I get a workaround.
I use the command
mount -F nfs -o rw,proto=udp radiohead:/export/home /mnt/radiohead

You know, the difference between these two times is the use of option "proto=udp".

When using RH3, I can mount the Linux without this option. Can anyone tell me what is difference between RH3 and RH4 that cause this problem?

thanks.