Rooftree
I'm with scook on this. I really liked Pentagon, but I had nothing but trouble with it. After far too many wasted hours I finally realized my time would be better spent using a stable synth than fighting to make an unstable one work occasionally. I hate to say it, but if you're having trouble with Pentagon (besides the administrator privileges issue) you're best off running far, far away from Pentagon. Rapture is on sale for only $20. A small outlay of cash on a stable synth will allow you to make music instead of fight with your computer.
Rapture is a very nice synth, and in many ways it is more sophisticated than Pentagon, but I don't think it can be considered a replacement. Z3ta +2 is also a very fine synth but again, not quite the same territory as Pentagon.
The Korg legacy collection
Mono/Poly is realativly inexpensive, has recently been updated to 64 bit and if you like Pentagon, you will like this one.