Hilary,
I have solved the problem, but only after I set this down, walked away and worked on something else for a couple days...
I opened the form in designer today and noticed under File | Info | Form Template Properties that the Name had somehow changed to ActualFormName_OLD. I changed this back to the actual form name and republished and now all is well and I get to keep my job. :)
I typically save form templates on my local with suffixes, but I never change the internal form name. I checked some of my other forms and they have unique external file names but all have the same internal form name so at this time I have no definitive root cause of the internal name change, but I will never forget this lesson...
Thank you so much for your help in this matter.
-Don