So, a couple of totally different things you can try:
Create an audio signal from an empty workspace via Generating > Tone. Save this tone to two separate mp3 files in a totally separate directory. Does your macro fail with these files?
Run Tools > Reset Configuration, and try again.
Close Audacity, then rename your audacity settings directory by:
a) Click on the magnifying glass in your Windows Toolbar and type %appdata%
b) Rename the audacity sub-directory to audacity-hold (note this will move your Macros directory, so you will also have to reenter your macro).
c) When you startup Audacity, it will create a brand-new audacity setting directory. After your test, you may wish to delete this new audacity directory and rename audacity-hold back to audacity.
If none of the above steps fix the issue, post the macro here (it may still be in your audacity-hold\Macros directory created in the previous step).