When you set the OnLayoutLoad script trigger, not only can you select the script (which you have done), you can also specify which modes to enable the trigger.
The default for the OnLayoutLoad is that the trigger is enabled for Browse mode only. This means that if you return to the layout when in Find or PReview mode, the script will not trigger.
I suspect that you need to go back in and enable it for Find and Preview modes too. ;)
BUG REPORT: When you set the OnLayoutLoad script trigger in FM11 Pro on Windows 7 64 bit and that is set on the form you are editing and you go to browse mode, the trigger doesn't fire. If you switch to the form from another form, it does. It should always fire!