Hi, i found something on IBM.

I add my user with total control (yet in the admin groupe) on the register key
HKEY_LOCAL_MACHINE\SOFTWARE
HKEY_LOCAL_MACHINE\SOFTWARE\IBM
HKEY_LOCAL_MACHINE\SOFTWARE\IBM\ADSM

Right clic, autorisation, select my user in use and put him the total control.

Since i do that i have no popping password.

Source:
http://www-01.ibm.com/support/docview.wss?uid=swg21456125

Continuous Password prompts during back up to a Tivoli Storage Manager server
When using a Tivoli Storage Manager server as the backup target, the 
application password prompt keeps popping up if the User account on the Client 
machine does not have administrative privileges. The reason is because Tivoli 
Storage Manager needs full access to every key in the following registry path 
in order to save the password:
HKEY_LOCAL_MACHINE\SOFTWARE\IBM\ADSM

To fix the problem, use regedit to grant full access to the user running Tivoli 
Storage Manager FastBack for Workstations. Full access must be granted to the 
following keys:
HKEY_LOCAL_MACHINE\SOFTWARE
HKEY_LOCAL_MACHINE\SOFTWARE\IBM
HKEY_LOCAL_MACHINE\SOFTWARE\IBM\ADSM

NOTE: For Tivoli Continuous Data Protection for Files 3.1.7.0 and Higher or
Tivoli Storage Manager FastBack for Workstations 6.1.1.0 and Higher Full access 
must be granted only to the following key:
HKEY_LOCAL_MACHINE\SOFTWARE\IBM\ADSM

Regards, Mickael.

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