There are some security restriction while registering plugins for MS CRM 2011 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. Only the System Administrator user account or any user account included in the Deployment Administrators group can run Deployment Manager.
For non-isolated plug-ins, failure to include the registering user account in the Deployment Administrators group results in an exception being thrown during plug-in registration. The exception description states "Not have enough privilege to complete Create operation for an SDK entity."
The system user account under which the plug-in is being registered must have the following organization wide security privileges:
The System Administrator role has these privileges. For more information, see Security Role and Privilege Reference and The Security Model of Microsoft Dynamics CRM.
For plug-ins registered in the sandbox (isolation mode), the system user account under which the plug-in is being registered must have the System Administrator role. Membership in the Deployment Administrators group is not required.
Please read this Article for Registering and Deploying Plug-ins in MS CRM 2011 using plugin registration tool.