In IE 11 the Adobe PDF Reader browser extension shows enabled but it is not running

On some workstations, we see the browser extension is enabled and currently loaded. On those workstations we have no problem opening an aspx file that is associated to open with the default pdf handler (Adobe Reader). On other workstations, the extension is listed as enabled, but it is not running, and we are not able to open the attachments which the other stations were able to open. How do I get the extension loaded? I mean in the computing sense, not the anthropomorphic frat boy sense.