Once in a while somebody needs to do that to fix a particular Windows permissions issue; a lot of it depends on how you have Windows configured, but you shouldn't normally have to do that.
What version and build are you using? If you don't already have Mixcraft version 6.1 build 204, give it a try. It's on Mixcraft's download page
If the problem happens again with the latest build, quit Mixcraft immediately 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