Error Stopping Qmail from Plesk Interface

[amandler]

When I stop qmail from the Plesk interface (for example, to do queue maintenance) it takes a very long time, over a minute, and then often gives this error:

"Server >
ERROR: PleskFatalException
Unable to make action: Unable to manage service by mailmng: mailmng: Service qmail failed to stop

0: /opt/psa/admin/plib/common_func.php3:174
psaerror(string 'Unable to make action: Unable to manage service by mailmng: mailmng: Service qmail failed to stop')
1: /opt/psa/admin/htdocs/server/restart_services.php:30"

However, the service DOES stop. Restarting is no problem. Anyone know what is going on here?

qmHandle is also giving errors when I try to use it saying it cannot stop the queue.

Thanks.