No export problem with v8.77 here - AVI, mp4, or MKV.
However, there were several issues...
1. The text to speech WAV file has an echo.
2. The 00007.MTS file 'rings' when exported (distorted audio). This is a reported bug. Sync was slightly off.
To fix it...
1. The WAV file was rerecorded and substituted for the original.
2. The MTS file was exported alone as an AVI with Mp3 audio, then the MTS was replaced by that AVI, and sync was corrected.
See your Personal Message for the revised project.
If it doesn't export then there is something local to your PC that requires further research. Just tested, and works fine here. Please report back.