Snipazer,
Please go through the link shared by Ahmed, I guess that will help you.
The NTUSER.DAT file is a registry file. Each user's NTUSER.DAT file contains the registry settings for their individual account. The Windows registry, as described by Microsoft, is a "central hierarchical database" that contains information about the software,
hardware and user profiles contained on a computer. Windows is constantly referencing its registry files throughout the course of its operation. The configuration of the "HKEY_CURRENT_USER" branch of the registry is supported by the current user's NTUSER.DAT
file.
I dont think you have to do so if user is local administrator in his machine.
I guess in crm outlook add-in is getting disabled every time user logs in into is system.
Regarding deletion of registry key HKCU\Software\Microsoft\MSCRMClient, please go through link : http://support.microsoft.com/kb/950175
BR, Rishabh Mishra