Netmail Archive 5.x
Outlook has disabled the Netmail Archive Add-in by setting a registry key. After which, Outlook will not attempt to reload it unless the registry key is fixed or the Add-in is completely re-installed.
Outlook will protect the user experience by disabling an add-in it considers to be misbehaving.
The following steps will help you determine if an add-in has been disabled, and how to re-enable it:
1) Click on the Windows Start button, and run regedit.exe (either through the search box in Windows 7 or using "run program" in older version of Windows).
2) Open the following key in the registry:
where (name_of_the_addin) is usually something similar to: M+ArchiveOutlookAddin.
3) In the right portion of the screen, you should see the values stored in this key. One of the values is "LoadBehavior". If the Data of this key is 2, then the add-in is disabled. You will need to set the value to 3 to re-enable it, and then restart Outlook.
Uninstalling and re-installing the add-in will also fix this issue. However, simply copying files as FTF files will not fix the issue.