3dsMax to Mudbox – Import Warning: UV not a complete set

I’m exporting my 3dsMax model to Mudbox. The import gives me a warning that the UV set is incomplete.

First, what does this mean? That I haven’t got all the UVs unwrapped? Web searches have brought nothing.

Also if this is the problem, is there a way to check if all UVs are unwrapped?

I’ll post my map if you need it.