There is no solution to loading the mod with whichever map you're trying to use it on. This is an engine limit error and you will not be able to play with both of them loaded.

If you're trying to play [MWZ] KILLHOUSE, it literally warns you in this big text near the top of the description:

If it's a different custom map, you're completely out of luck. This mod isn't made to work with custom maps, only Treyarch's. Some custom maps work, but it's not my goal to increase compatibility whatsoever.