Errors when adding new ship type to vehiclesizes.txt

I'm trying to add a new ship size to the game (a Battle Cruiser, set in between cruisers and Battleships) but I keep running into an error whenever I try to create a new empire while trying to start a new game. I'm getting the message:
"access violation at address 0056EEB1 in module 'SE5.exe' read of address 00000038". After X-ing out of the blank screen that pops up I then get this message:
"access violation at address 00702948 in module 'SE5.exe' read of address 00000014"
I eventually figured out that it seems to be a problem stemming from adding a new ship type to the vehiclesizes.txt file. After messing around a while I realized that if I removed the original empire types (terran, amonkrie, etc.) from the Empires folder and then start a new game it lets me create a new empire without crashing (the only one listed is my modded one, called manticore,). I did have to leave in the "default" folder because there are some AI text files in there that it was asking for.
Unfortunately, even though I could start a new game, whenever I tried to go into combat it would crash.
I know that the ships and everything work because I had tested an earlier game just using a saved empire setup, and the battle cruiser was there where it was supposed to be and it worked in the simulator.
I'm at a sort of catch-22 at this point. I leave in the other empires, but can't add or edit a new type, or I take them out and can't have any combat.
I guess I could just create and save the empire settings I need before using the edited vehiclesizes.txt, but that's more of a workaround instead of a solution. And who knows what sort of problems it might cause down the line.
Anyway, sorry for the long post, but if anyone have any ideas I could use the help.
Thank you.