OK, crashes in SC are caused mainly by two issues:
!)corrupted DAT files. In this case the crash happens most often at the very runtime of SC, or when you start a game.
@)invalid spriote animations. In this case the crash can happen pretty much at any time, whenever the wrong animation is called.
Reading from your posts I think that it's the latter case, so - as you suspected it well - you'd need to get in touch with Iscript. As for your 'buildings bug', this is in fact the very proper behaviour of the game because what you've actually changed were just the main graphics for a building, and you left all the rest (animations, working overlays etc.) untouched, so they are there just fine.
You'll need to enter the mysterious world of ICE/IceCC, but don't worry - this will be a fantastic journey, trust me. The effects that Iscript editing will allow you are incredible. For example you will be able to create 'critical hits' for your weapons, dealing several times more damage than a single strike! But there are much more...

Your first resource should definitely be SCEB (SC Editing Bible). Although it's old and incomplete - that's the best resource available (for the time being....in a not-so-distant future SCEB will be able to go asleep in the Starcraft Hall of Fame...)
http://www.campaigncreations.org/starcraft.../contents.shtmlBear with it for the beginning, and when it won't be enough - come and ask here,again
