no, actually I was pleased to see that on my test computer convert to MP3 worked great... better than on my music computer.

Which leads me to point out the fact that the MP3 export requires you to have an encoding codec installed on your computer (to my knowledge, the translation isn't built into BIAB)

If this same PC hosted BIAB prior to ver 2016, and it was able to export to MP3, maybe you need to tell BIAB the path to the codec. (I'm not at my BIAB computer at the moment, so I can't tell you the steps)

On the other hand, if you installed to a PC that has never exported to MP3 from within BIAB before, you may just need to DL and install a codec.

disclaimer: none of the above guarantees there isn't something else going on to cause the exception.. it's just a good place to start looking