Hi Michael,
Thanks for the added information about rendering to mp3. That's a different problem.
With mp3s...
If you want to use BIAB to create mp3s, it's necessary to install codecs that will translate a WAV file into an mp3 format.
This is because neither BIAB nor Windows come with the necessary drivers to do the conversion. (Up until just recently, the mp3 format was protected by patents.)
When I need an mp3, what I do is to use a freeware program called FreAc. It's a very comprehensive program and gives a great deal of control over the resulting mp3. I simply load the wav into and then convert.
https://www.freac.org/Alternatively, if you download and install K-Lite (freeware), that will install the necessary mp3 codec (just be careful of installing any unwanted software that might be attached to the download).
Lastly, unless the mp3 format is an absolute must, try rending to wma as an alternative. Since this is the Windows format, drivers are present on all Windows systems and there won't be any problem rendering to this format. The wma format is comparable to mp3. It's the same size and I personally think it sounds slightly better.
Hope this helps,
Noel