Working around CRM2011 Error Message “Unable to load the plugin type”

Working on a CRM 2011 solution during a migration from CRM 4, I tried to upload the solution and watched the green progress bar reach about 80%, when the install routine decided that it’s time to rollback, and decreased the progress bar again.

The upload log showed the error message “Unable to load the plugin type”, as reported by others here and here and everywhere.

Since all my work of the day would have been lost, I tried to track down the cause of the error:

Using the Plugin Registration Tool, I saw that all the steps of one specific plugin assembly where disabled, since the assembly had not yet been upgraded to CRM 2011.

I could remove the plugin assembly from the solution I was working on, but I could not uninstall it. I figured out I had to modify the solution.zip I wanted to upload.

First, I removed the PluginAssemblies directory from the zip file.

Next, I edited solution.xml, and removed all entries starting with

      <RootComponent type="91"

as they refer to the plugin assemblies which are now removed from the zip.

Finally, I edited customization.xml, and removed the sections

  <SolutionPluginAssemblies>
    <PluginAssembly.... >
      ...
    </PluginAssembly>
  </SolutionPluginAssemblies>
  <SdkMessageProcessingSteps>
    <SdkMessageProcessingStep ...>
      ...
    </SdkMessageProcessingStep>
  </SdkMessageProcessingSteps>

After moving the two files to the solution.zip, the upload performed successfully.