mount: server:path failed, reason given by server: Permission denied

We get this peculiar NFS moount problem for quite a few reasons. But recently we encountered this problem and scratched our head debugging it. We tried restarting nfs server (service nfs restart), exportfs, validating /etc/export of server. Nothing solved the issue

engweb:/mnt/kits# mount -a
mount: library-hq:/export/kits/ failed, reason given by server: Permission denied
mount: library-hq:/export2/kits/ failed, reason given by server: Permission denied


But the actual issue is root partition (/) was full in the machine which hosted nfs server. After clearing the disk space everything got resolved.