Honeywell FMC 757
I hope this in the right place.
FMC all loaded properly with PERF INIT and TAKEOFF data loaded.
Message shows MAX ALT FL XXX, if you go to clear it in the scratch pad your initial fuel will show, but no fuel calculations will show up on LEGS or PROG.
In order to get the calculated fuel back you have to change the cruise altitude on the VNAV page to something it will accept, if the cruise altitude up link was more than what the FMC allows.
This was not taught to me in school nor passed to me on the line, the engineers couldn't figure it out either, I know it seems obvious now, but forgive me I'm a slow learner.