Yeah, that's a bug. I was just searching to see if others had this issue. There are a couple other areas that don't lite up the execute button and give the appearance of a lockup. I found a temp fix. Press the execute on the FMC in the sim. The screen then sync's/refreshes. I've been trying to report this to Winwing, though there chat system / website does not seem to work well. I can't get a chat box.