HaloMods "Classic" Read-only Archive

Whenever I try to open a sandbox map variant with forge i get the message:
"Object reference not set to an instance of an object"

I tried several different variants including the original map as it was with a few things added. Every time, I get the same message.
What do i do? Thanks for any help.
-Sorry if this was answered somewhere else, if so I could not find it

Forge doesn't have the Mythic maps xml's so it cannot load the tag lists.

Oh, thanks