Inappropriate ioctl for device MSG=cannot create job file for Torque

I encountered this error on the cluster.

qsub: submit error (PBS_Server System error: 
Inappropriate ioctl for device MSG=cannot create job file 
/var/spool/torque/server_priv/jobs/497741.headnode-h00.cluster.com 
(28 - No space left on device)) 

I did a df -h and notice that there is still space. But when I did a df -i, I've noticed all the spaces iUSE% is almost 100% used up. To bring up the

# find / -xdev -printf '%h\n' | sort | uniq -c | sort -k 1 -n

References:

1. Find where inodes are being used