Cross threaded/stripped bottom bracket
You probably didn't remove material when you cross-threaded the bottom bracket shell in.
If it's a steel frame, you can cut new (correct) threads with the correct taps. The taps are quite expensive, (they have to line up, and one is upside down, find a shop or local framebuilder who has one.

Baring that you should chase the threads : grab old steel bb shells, cut two triangular grooves in them. You want a perpendicular cut on the trailing side of the thread. (Ask the internet for images of a thread chaser). Fill the grooves with thick grease, thread them in and out wipe it down and you're done.

You can wrap some teflon tape around the threads to make them tighter as well.

Either way you probably shouldn't "invest" money on this frame anymore, maintain it and once you've ridden it through, turn it into a shop stool.