Hm, sounds strange indeed. My first guess would have been a name resolution issue - but you mentioned that you had tried mounts via IP already.

I remember having had difficulties between an old portmapper and a new libtirpc client... iirc it had to do with trying tcp instead of udp (hence my first suggestions). But that's years back. Could you please also try with "-o udp" (as an alternative to "-o proto=udp"), just for completeness' sake?

You'll find someone with the same symptoms here, and that's from 2002... but then, the thread opener resorted to upgrading