in both Chrome and firefox there is a button between that gives an error. In apache2 error.log it shows: "Premature end of script headers: is.pl, referer: http://srserver_ip/lsmb14/is.pl"
Thanks for reporting! The button - by the way - is the "Hold" button.
This issue has been fixed. It was the "On Hold"/"Off Hold" button that didn't have any text.