If you are not able to start OpenVZ VPS because of a Quota problem, then you can follow the steps given below:
# vzctl start
Starting container …
vzquota : (error) quota file is corrupted
vzquota on failed 
Here is a dirty quick fix
Turn off quota
– vzquota off (or vzquota off -f)
– vzquota drop
Restart your VPS.
Note : You have to put the correct VPS number.