I'm performing a quick resurrection for anyone who's having issues with apocalypse. I got a couple of random game crashes, and a bunch of 'please reinsert the x-com CD' freezes with no other option than to quit and reboot, but I found a solution.
-In the C:\Program Files (x86)\Steam\steamapps\common\xcom apocalypse folder, there's a CD image (conveniently labelled "CD"). Mount that in your favourite tool, open up E:\XCOM3 (replacing E: with applicable drive letter) and copy all of the folders (not OPTIONS.dat or XCOMAPOC.exe) into \steamapps\common\XCOMA.
-Under the Steam client, right-click and remove all game data. Then re-download - it shouldn't have to go through the whole process again, so it won't take long. Now your Steam folder will be slightly bigger, but your apocalypse games won't run into that irritating error any more.
Won't help you with the difficulty though - I never got far into this game before, simply because I kept getting stressed at my rate of death. Even now I can only keep up with it by glitching myself some cash when I run low - another trick I've found, though it'd probably be all over google if I bothered to search. Set your workshop to a project, and okay it back to the main research screen. Select reassign, and then okay back without changing anything - you get the cost of the project back. A pain in the arse when you're doing it with $700 bio-transport modules, but a lifesaver when you need the cash.
Please note that I tried the above CD error fix once, when I discovered it worked, and haven't tested it again since. My saved games remained in the system (not for long - accidentally took out a police HQ and Osiris base, and they raided me to death) and all I had to do was reset the resolution back to 1920x1080. It worked for me, but I claim no responsibility for it not working for you. Interesting to see if it does, though.