STEPS:
1. go onto game
2. select civ (new/old)
3. select custom bldg/unit
4. GAME CRASHES

Whenever I make a custom civilization, I make a unique unit and unique building (UU/UB). When I want to build them , the game crashes! This happens every time and is costing me time, and I really want to post my mods on the forums. I also created a new unit (not a civ UU) and the game also crashes when I click on it...

Could it be related to this prob?

Have you checked your artdefines.xml? Maybe that is the problem, if you are linking the unit or building to an artdefines that doesn't exist, then the game will crash.

YEah, here's a list of what I checked:
-all the XML files in Units, Bldgs, Civs, and Art folder
-file structure
-I made sure I posted in CityLSystem and FormationInfos

+The art appears in the civiliopedia