Hi Nigel,
I think this problem was related to the strange license activation problem you had before. For some reason things got messed up in an odd way. As Carlos and Sander have noted, the standard solution to these problems is resetting PI's configuration (launching with Ctrl pressed is a useful backdoor). However, this certainly should not happen. I'll take a good look at the installation and activation routines before the next release.
On the other hand, installing on an arbitrary directory is (should be!) perfectly possible and should cause no problems. However, the standard C:\PCL (C:\PCL64) location is recommended. Anyway, PI installations and directory trees will change in the near future, so we'll have new issues...
![smile :)](http://pixinsight.com/forum/Smileys/default/smile.gif)