PSP 9 won't work in Windows Vista

Question

I prefer PSP to all the other versions. I installed it on my pc - which is Windows Vista - (Dell XPS 420) and it just stops working. No explanation as to why. The thing I can't understand is that I was able to install Version 8 and Studio - so why is PSP 9 giving me problems?

I had it on Windows XP Professional and it worked fine - then I started to get this same message. At first I thought my own copy was corrupt or something, but I obtained another copy of Paint Shop Pro 9, installed it and I'm getting the same error message - PSP has stopped working. That's it - the total message. Any ideas?

Thanks!