You must make sure that u use the correct format though and size. I you have photoshop ot similiar a good tip is to load one of the decals that are already create delete the picture then substitute your picture then save it under another name.
That's a hell of a lot of work you're doing there Confused!
Just make sure that you're decals are .tga, and under 5k in size. Size options are either 32x32 or 64x64. That's the basics. I've done quite a few of the "actual" BT unit decals for myself, as I was a long time PnP Battletech player about 10 years ago.
Never argue with an idiot, they will just drag you down to their level and beat you with experience.