I've decided to start a database of all the known errors of all CC games. Post here any errors that you know of that aren't on the list and I'll update the top post so everyone can have a one-stop-shop for error solutions.
Unable to Format Stream
This is a video error. Close Combat versions CC3 - CC5 use the outdated Indeo video codec to play starting videos and cutscene videos. You can fix this problem by installing the Indeo codecs from the downloads page. They are in the "Other" section.
Close Combat Error
This is a data error. If you have edited any game data files, then something you edited is incorrect - either a value is out of the range of acceptable values (like putting 300 for "vehicle type" when there are only 100 vehicles) or you made a programming error like making a squad with 5 soldiers but only setting the type for 4 of them. Check your data!
If you get this error but you have not edited any game data, reinstall the game and this problem will go away (but you might have other problems besides this one that still need attention).
Close Combat CD is required
This error occurs in two cases: You don't have the CD in the correct drive (it searches for the CD in the drive you installed it from) or one or more game files is missing from your Close Combat folder on your hard drive. For some reason if you take a necessarry file out of your game directory, the game returns a "cd required" error instead of telling you "data not found" or something else helpful. Either replace any game files you moved or reinstall the game and this problem will go away. This and other problems can be caused when installing mods using the mod manager when the plugin does not uncompress correctly.
Can't Find the Directory: Videos
This error occurs when installing mods. Uninstall CCV, reinstall CCV, install the 1.05 patch, create a folder in the main CCV directory called "videos" and then install the mod again. This and other problems can be caused when installing mods using the mod manager when the plugin does not uncompress correctly.
Informs DirectDraw that...
This is a DirectX error basically caused by CC being an older game. It's a simple fix, by going to c:/windows/system32/dxdiag.exe (or go to Start>Run> and type in dxdiag.exe) and on the Display tab click Disable next to Direct Draw. You can go back and re-enable it any time you want to run a more modern game. I personally just created a shortcut to dxdiag.exe on my desktop since I play so many different games.
Invalid data in Battle and Unable to find Operation in Data.
These are caused by a campaign or battle file being missing or in the wrong folder. When the game starts up it searches for all the battles, operations and campaign files. If it doesn't find the ones it's looking for then you get this error and the game crashes. Can be fixed by reinstalling the game. If you only get this error when running a particular mod, make sure you have the latest version. Unfortunately there's only one good fool proof way to make sure you have all the battle files if you're missing one - reinstall. This and other problems can be caused when installing mods using the mod manager when the plugin does not uncompress correctly.
Out of Hard Drive space
This error is caused when map files are missing or corrupted. downloading the correct maps and installing them manually will fix this error, if you know which maps are possibly causing the problem. If you don't, then reinstall the game and patch and the game will work. Install your favorite mods one at a time and when you get the error you know which mod is causing the issue. If you haven't installed any mods then the problem is a map you downloaded that is missing one or more files or is corrupt. This and other problems can be caused when installing mods using the mod manager when the plugin does not uncompress correctly.
Can't access Surface for lock
This is a video driver error. Obtain the latest video drivers for your video card, and make sure DirectX Direct Draw is disabled (as mentioned in "Informs Direct Draw" above). You can also try adjusting your hardware acceleration by Right clicking on your desktop, and going to Properties>Settings>Advanced>Troubleshoot and lowering or increasing hardware acceleration.
Crash with no error message when starting battle
This is caused when a tank, gun, wreck or shadow graphic is missing or incorrect. If you're a modder, go back and use your last known good backup (you keep sh1tloads of backups, right!) and re-do the last change. If you're a player then make sure you have the latest version of the mod you're playing.