Problems with the export of certain of parts to audio files

Hi!

I wrote a score for a marching band. With File > Parts I created parts for each instrument. The problem is that when I try to export parts to wav, flac or ogg file via File > Export parts, only certain parts gets extracted. For example, parts for Clarinet in Bb and Trumpets and a few other instruments won't get exported - the message "Cannot write into C:/" pops up.

However, I can export all parts to mp3.

I'm using Musescore v. 2.0.3 on windows 7 32 bit.