Error loading mixed mode assembly

Mar 16, 2011 | 1 min read | C#

Referencing a .N2.0 assembly from my .Net 4.0 client profile application today I encountered this error:

Mixed mode assembly is built against version 'v2.0.50727' of the runtime and cannot be loaded in the 4.0 runtime without additional configuration information.

What is this additional configuration information? Add

useLegacyV2RuntimeActivationPolicy="true"

<configuration>
  <startup useLegacyV2RuntimeActivationPolicy="true">
    <supportedRuntime version="v4.0"/>
  </startup>
</configuration>

For more information, see this excellent post.