I wanted to pass along my experience in case anyone else has trouble like this. I have the Bigfish version of Plant Tycoon, and could not get the Virtual Seed Tray to open. I looked through all these posts, and couldn't quite find the exact same problem. The error message I was getting after updating the Microsoft .Net guide thing to 4.0 was "Unable to find a version of the runtime to run this application". In desperation, I tried downgrading the .Net from 4.0 to 3.0, and now the VST utility works. I also had the same problem (unable to open) with the Constant Gardener utility, and this seemed to fix that problem too.