The problem is that the wav files you are importing are being seen as unsupported .wav file type by BBM. This can be true even if the file is 44.1khz and 16 or 24 bit. It has something to do with compatibility for 64bit systems vs 32 bit systems. Read this thread:
The easiest way that I have found to resolve this issue is to run wav files through a format conversion program, such as NCH Switch. Simply convert your existing wav file to the the 16bit 44.1khz format offered in NCH Switch, and then the wavs will work. This is the RF64 compatibility issue mentioned by GoranGrooves.