Replace the relevant bits in your nunit-console.exe.config and nunit-gui.exe.config with this:


<startup>
  <supportedruntime version="v2.0.41013" />
  <supportedruntime version="v1.1.4322" />
  <supportedruntime version="v1.0.3705" />

  <requiredruntime version="v2.0.41013" />
</startup>

BTW, the config files live with the .exe files, e.g. in C:\Program Files\NUnit 2.2\bin