PDFMaker Office COM addin not able to attach to emails

I am attempting to mail merge names into a document to create individual certificates, and then email those certificates to each individual, all through the PDFMaker addin in Word (sending the emails through Outlook).  This worked fine for me until a couple of weeks ago.  Now, every time I try it works for the very first entry, but I then get an error message (see image below) which repeats for each additional entry.  I have this issue on multiple computers. Is there a solution to this issue?

I am using:

• Windows 7 Professional
• Microsoft Office 365 ProPlus v16.0.6741.2063
• Adobe Acrobat XI Pro  v11.0.17.9

I (and my IT support at work) have tried the following:

• Uninstalled and reinstalled Adobe Acrobat 11 twice by first uninstalling Adobe Acrobat through Control Panel and also have run the Adobe Acrobat removal tool to clean up any files left behind by performing a standard uninstall.
• Uninstalled and reinstalled Office.
• Performed a System restore on the Windows Operating System which failed.
• Disabled and re enabled the Word Add in for Adobe Acrobat which made no difference.
• Tried a fresh merge list (in Excel) with a fresh Word document.

Thank you.