Plug-in assembly does not contain the required types or assembly content cannot be updated

There are a number of reasons why you might receive this error when deploying a CRM Solution to a new environment. One of the more obscure ones is that one of the Plugins contained within the Solution is registered with Isolation = None and the person doing the deployment is not a Deployment Administrator.

A CRM Organization System Administrator can deploy solutions that contain plugins only if the plugins have an Isolation Mode of Sandbox. If it is set to None, then this additional security grab requires a CRM Deployment Administrator to undertake the deployment.

Screenshot of Dynamics CRM Plugin Registration tool showing Step 3: Isolation settings

This of course is a Dynamics CRM 2011 / 2013 / 2015 / 2016 On-Premises scenario as you can only deploy plugins to the Sandbox in an Online environment.

For more info, see Walkthrough: Register a plug-in using the plug-in registration tool