RRDTool
From ATI public wiki
RRDTOOL
ERROR: could not lock RRD
Appears due to broken NFS locks
Usually after abnormal network outage between NFS storage server and client system where RRDTOOL works
Fix
mv dbase.rrd dbase.rrd.old
cp dbase.rrd.old dbase.rrd
rm dbase.rrd.old
Another fix
restart both servers