I ran into this same problem and was receiving the following error:
[root@serverid]# vzctl start <veid>
Starting VPS ...
vzquota : (warning) Incorrect quota shutdown for id <veid>, recalculating disk usage
vzquota : (error) quota check : lstat `conf': No such file or directory
vzquota on failed [1]
I fixed it by running the following:
[root@serverid]# vzquota off <veid>
vzquota : (error) Quota is not running for id <veid>
vzquota : (warning) Repairing quota: it was incorrectly marked as running for id <veid>
[root@serverid]# vzquota on <veid>
By turning the quota off and on for the account I was then able to start up the account with no problems.