I had trouble with this and you can read quite a bit of advice here:
http://forum.cakewalk.com...10&mpage=1#2323721 In short, this was resolved for me by 1-opening guitar rig in stand-alone mode, 2-going to service center, 3-ignoring the message that says all products are activated, 4-clicking on options and then 5-registering the product with the serial number emailed at the time of the upgrade.
This is NOT obvious since service center tells you all products are activated and Options does not seem like the most logical place to click to upgrade. NI is aware of this usability issue.
I hope this is the same issue you are having and that this will help. I really like Guitar Rig 4 now that it works, but I got very upset by the confusing instructions--or rather the lack of instructions--provided by Native Instruments. Technicians tell me that NI is a good company but it has grown too fast and they don't yet have the staff to support all their sales, so hopefully things will level out soon. (It took me 5 days to get an answer from them.)
By the way, since my lead-playing skills are not really equal to my keyboard skills, I use RealStrat from MusicLab and it is awesome with Guitar Rig. I assume an actual Strat with a good player would be even better. I tend towards slightly warm tube sounds with just a bit of drive, but Guitar Rig will get as crazy as you want.
post edited by konradh - 2011/06/18 12:34:47