Doc Merge - just stops

Testing out Doc Merge in our V12 production system.  This is the first time experimenting.

We built a small Word doc (DOCX) and loaded in some Account fields (name, address, etc.).  Then ran Doc Merge.  The dialog pops up and the progress bar is about 20% of the way across - and it just stops.  And sits there.  Forever.

We downloaded some of the example templates ( and uploaded it into our site.

Selected to run it against an account and got the same thing...progress bar is 20% and then stops.  Forever. :-) 

There are no messages in the system log.  There are no messages displayed in the UI.  Can't find any information on troubleshooting it.  Any guidance would be greatly appreciated.  Thank you!!