Try re-installing, then try loading Pianissimo and if the same thing happens, quit Mixcraft and send us your mixcraft-log.txt file, which is located in this folder:
Another way to find it is to click on the Windows Start Menu, select All Programs, then Acoustica Mixcraft 6 (or 5) and finally Logs. Submit an Acoustica Support Request
and attach the log file along with a brief description of the problem.
Here's a short video: Mixcraft Mini-Tip: How To Find Your Mixcraft Log File