Normally the IPL is accessed by holding the 2 right-most keys on the LCD screen during boot.
Like this video shows....
http://www.youtube.com/watch?v=6HlQn-QCKJE

This worked fine in the past but now it doesn't work and just locks up the control. If I power off/on the machine boots fine as usual and works perfectly. Any ideas what would cause the lockup? The machine is Mori SL-253 with MSG-500 (Fanuc 21iT-A) with Mori MAPPS panel