A VPS is locked when some operation (backup, migration, start / stop,
etc.) with that VPS is in progress. You can determine which process is
holding VPS #101 using the following command on the hardware node:
cat /vz/lock/101.lck
You can kill that process if needed, but make sure that the process is
really killed. If there is no process with that PID on the node, just
remove the lockfile.