Hi Mike,
I think v3 but I'm not sure (how do I check this?). At any rate, I tried your suggestion both ways
[root@mseas etc]# mount -o vers=3 mseas-data:/home mount.nfs: Unknown error 521
[root@mseas etc]# mount -o vers=4 mseas-data:/home mount.nfs: mounting mseas-data:/home failed, reason given by server: No such file or directory
What should I look at next?
You appear to be missing the target mountpoint in your manual commands. It should probably look more like:
mount -o vers=3 mseas-data:/home /home
On the other hand, a Google search for "mount.nfs: Unknown error 521" turns up some interesting information:
https://www.google.com/search?q=mount.nfs+unknown+error+521&ie=utf-8&...
One of the items is a bug report from Fedora in which it turns out that the /etc/exports file has some sort of corruption (probably invalid characters) in it that was causing the NFS server system to not properly export the filesystem.
You may try, on the mseas-data system, to run "exportfs" to see what the system thinks it's exporting.