Please download this file:
Save it in you Yawcam directory. (Typically C:\Program Files\Yawcam)
Now start Yawcam by using debug_start.bat and try to make the movie again. Yawcam will now create a log file with some debug information. The file will be called: debug_log.txt
Please send this file to me.
Oh, I forgot... It's possible that you run into some permission problem if you are running Windows Vista or Windows 7.
To overcome this you will need to start a command prompt as an administrator, and then run debug_start.bat from this command prompt.
You start a command prompt as an administrator like this:
Click on windows start button.
In the search field, type: cmd
Right click on cmd in the result list and choose "Run as administrator"