Transparent lightmap problem

I actually remember having this problem awhile ago, but can't remember the fix. I've tried to find the topic about it, but unfortunatly, I couldn't locate it.
Anyway, I just lightmapped a bunch of objects in my age. In URU, they all look fine except for one; this one is black, and transparent. (even though there's no alpha on the object.) The lightmap is applied correctly to the object, in Map input it's set to UV and Lightmap, and in Map to, it's set to Multiply like it should be. Anyone know what might've caused this? I seem to remember something about the Map to buttons, but I can't put my finger on it...
Anyway, I just lightmapped a bunch of objects in my age. In URU, they all look fine except for one; this one is black, and transparent. (even though there's no alpha on the object.) The lightmap is applied correctly to the object, in Map input it's set to UV and Lightmap, and in Map to, it's set to Multiply like it should be. Anyone know what might've caused this? I seem to remember something about the Map to buttons, but I can't put my finger on it...