CRM 2011: Plug-in assembly does not contain the required types or assembly content cannot be updated

This error message might have various meanings; here is the problem I had and how I resolved it:

Problem: 

on registering a plugin assembly by using plugin registration tool system throws this error:

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

Not a very clear message and it took us some time to figure out what happened. We have a team of 5 developers using TFS to implement the code, when I wanted to register the plugin, I've got the latest version from TFS and build the assembly.

How to solve:

When you are trying to register your plugin #2, you can see the plugins within the assembly, compare the plugins with the ones that are registered and you may find out the registered assembly has extra plugins which does not exists in the assembly you are trying to register.

We had this issue because one of our team embers registered the assembly but did not checked the latest version in TFS so when I got the latest version from TFS there was a plugin missing from my assembly in compare of the one her registered before.

PLEASE COMMENT IF THIS WORKED FOR YOU