This is just a recent change but when trying to convert a WMA file to an MP3 file fails on our server, with the error "The specified source format could not be read."
I have tested on my laptop and desktop here and verified they can convert WMA to MP3 with no problem. Switch has also made this conversion in the past (it is a test vector file which we used in the early testing with success), and only recently has begun to fail to convert WMA files.
I read around here that it might have to do with remote desktop audio settings but even trying all 3 choices (leave sound, bring sound, do not play) does not yield a working Switch.