switching to user in usermin causes a error

Using the //switch to user// feature UM for admin we get a error....

Invalid PID file
Call Stack Trace
File Line Function
./usermin-lib.pl 83 usermin::error
/usr/share/webmin/usermin/switch.cgi 23 usermin::reload_usermin_miniserv
(eval 87) 6 (eval)
/usr/share/webmin/miniserv.pl 2105 (eval)
/usr/share/webmin/miniserv.pl 733 miniserv::handle_request

Status: 
Closed (fixed)