There is a problem with Acrobat/Reader. Error (0:104)

[Sierra69]

We have an issue with several users and PCs when they click a URL link to a PDF document they will get this error in IE:

There is a problem with Acrobat/Reader.  If it is running, please exit and try again. (0:104)

OS: Windows 10 Ent. x64

Browser: IE

Adobe Reader Version: DC v19.x

Scenario:

• Opening PDFs directly in Adobe Reader works fine.
• Opening URLs in non IE browsers works fine.
• Disabling the Adobe add-in in IE opens the PDF OK (Although externally in Reader, and not in the browser as desired).
  
  
• Setting the 'open in browser' option to use another program (ie PDFDocs) works OK.
• Adding the URL host to the 'Privelidged Locations' in the Reader preferences under Security (Enhanced) allows the PDF to open in the browser as expected.
  
• Changing other Security settings in reader does not fix the issue.
• Uninstalling/Resinstalling Reader does not fix the issue.
• Running a Repair installation of Reader does not fix the issue.
• Clearing the Users Adobe preferences (C:\Users\Appdata...) does not fix the issue.
• Using the Adobe Acrobat Cleaner utilty (AdobeAcroCleaner_DC2015.exe) does not fix the issue.
• As far as I know, none of our group poliy settings for Adobe reader have changed in a long time.
• I'm not certain, but this seems to only appeared since updating from DC v18 to v19

This is getting very annoying for multiple users.  Somebody smarter than me please give us a solution.