Many many times we see where people are trying to upgrade pt3 from a previous version of pt3 and when they run the install file, they get an install error which says "error opening file for writing". It will look like this below:
The reason for the error is that pt3 is still running! Notice in this picture, behind the installer is the pt3 window which is telling the user to upgrade. You must close this window and exit pt3 BEFORE you try to install or you will get this error everytime.