Hey forum I'm having trouble installing the Dark user Interface on the Oblivion Mod Manager, I can install every other MOD but this one :/
Any tips on how I can successfully install it?

I think some of the UI installers need that you check the "Allow additional script types" checkmark under OBMM's Settings. Maybe that's your problem?

Do you get an error or does it just not run the install?

Perhaps a bad file. Redownload omod or if it is an archive make sure it has omod data in it to create omod.