Acrobat XI Pro - can't edit a form from another version of Acrobat?

I've got a form I'm trying to edit to see how something worked with a form field.  However, I can open it just fine in XI Pro, but when I do a Forms/Edit I get the following popup message: "This form cannot be edited in Acrobat. Please use Adobe LiveCycle Designer to edit this form."

I can open it just FINE on my old machine that has Acrobat 8 Pro with LiveCycle with no problem.

So, how is it that I can open AND edit this document in 8 Pro and not XI Pro??  I've been tinkering with a couple of different forms in XI Pro, and I assumed that LiveCycle must have been subsumed into Acrobat XI Pro itself, but this mystery would seem to indicate otherwise!

Help?  Answers?  Thoughts?  Cookie recipes?

Thanks!!