Making NUnit 2.5.5+ work with .Net 4.0

It seems that many have found NUnit 2.5.5 not working with DLLs compiled with .net 4.0. NUnit 3.x has been designated to work with .net 4.0; till that time make a modification to the NUnit config file and add this startup element under the main configuration element :

<startup>
<requiredRuntime="v4.0.30319"/>
</startup>