Sorry for necroing the thread, but I'm having the same problem of check_quota not displaying the quota. ispconfig latest, fully updated debian wheezy (based on perfect guide).
Installed the plugin correctly (+compatibility plugin without patching, since that's what it said in the readme) and I've enable troubleshooting in the check_quota plugin (bottom of config.php.
This is the output at the bottom of the troubleshooting page:
IMAP Quota Output
IMAP Command Sent: a001 GETQUOTAROOT "INBOX"
IMAP Response Received: Array
As far as I understand, it just cannot get the quota value from the imap server (dovecot). No errors in the logs.
Does anyone have any idea as to why? How did you get it to work as expected?
EDIT: For future reference, if you don't get the quota to display, it means the user has no quota *facepalm*