Forms :: Alert Windows Appear To Be Hidden And Application Locks Up

I have a forms 11g application that of course has several message and alert windows that pop up when various errors or messages need to be displayed. This all works great on the developer machine, but when I try and run the form on another machine using any browser the message and alert windows appear to be hidden and the application locks up with the rolling bar across the bottom. I would guess it is waiting for a response, but I cannot get the window to appear.

Following is an example of an alert to be displayed:
declare
vAlertButton number;
begin
vAlertButton := show_alert('NO_EMAIL');
end;