Hi Arnaud,

Thanks for the replying!

For the first question, I don't know in which scenario, the un-installed add-in will affect the excel execution.

For the second question, each COM add-in has its own registry setting for the startup type. This two kb article will introduce the difference between
the two types of add-in.
291392 INFO: Excel COM Add-ins and Automation Add-ins
http://support.microsoft.com/?id=291392

290868 HOWTO: Configure an Office COM Add-In for All Users on System
http://support.microsoft.com/?id=290868

For the third question, if the message is shown in the assistance window, I'd suggest you can disable the assistance.

Please feel free to let me know if you have any further questions. Enjoy a nice weekend!

Wei-Dong Xu
Microsoft Product Support Services
Get Secure! - www.microsoft.com/security
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