Comment 66 for bug 213444

Had the same issue mount.nfs: internal error

spent about a day trying different things, turns out our nfs could not do a reverse lookup on the client's IP. Resolv.conf had an old server not maintained by us and went away. Added a line for all the hosts that need nfs on the /etc/hosts of nfs server. mount -a started again.

Hope this helps some of you having this issue, because it was driving me crazy.