I confirm this as a bug, I am able to reproduce the error on my machine using medium trust.
Apparently this line of code causes the error under medium trust:
litDotNetVersion.Text = System.Runtime.InteropServices.RuntimeEnvironment.GetSystemVersion();
I will have to wrap a try catch around that for the next version. In the meantime it just means you can't use that system information page, it will not affect anything else.