Audacity is free audio editing software that is easy to use. If you have an audio file that won't play in Express Scribe, try opening it in Audacity and then exporting it. This often solves the problem. If the problem is resolved, be sure to upload your new audio file so the transcriber who checks the file will be able to use it.
If this initial step does not solve the problem, write a post saying the audio file won't play in Express Scribe and notify Heidi for more troubleshooting.