That isn't an ubermode problem, most likely. Failure of units to spawn is typically caused by having more command posts listed in the script than exist in the map, or a similar problem (syntax [spelling] error somewhere in the script. Make sure all the names of things are the same as what's listed in the script (names of cps [by default cp1, cp2, cp3...], names of units [all_inf_rifleman, etc], names of unit classes [these are specific designations, such as soldier, pilot, marine, special, officer])

Jaspo is correct. Uber mode is not to blame. When you click on the special class when it's unlocked does it say "Unit count 'blablabla 1-4 -or- 0'" if it says zero then no AI players are playing that character, if it says > 0 then you just can't find the ai players, i.e. cp's are underground or something. I'm assuming that your lua is setup correctly, though you should post it