I got an error whilst trying to register a plugin, saying the assembly must be registered in isolation.
I found out something which I had forgotten, basically only Deployment Administrators can register plugins which do not run in isolation mode (e.g. in the sandbox).
The user I was using although was a System Administrator in CRM wasn’t in the deployment managers group so could only register plugins in the sandbox.
luckily for me the CRM in the field blog had a detailed article on the subject which you can read by clicking the link below
This bit below I found very interesting
In the Security Restrictions section of the following MSDN article it states, “There is a security restriction that enables only privileged users to register plug-ins. For plug-ins that are not registered in isolation, the system user account under which the plug-in is being registered must exist in the Deployment Administrators group of Deployment Manager.“
Register and Deploy Plug-ins