Cannot create classic Tween in Adobe Animate

Question

I am trying to do a basic walk cycle in Animate using classic tweens. For the most part, it works. However, when I try to tween the character's muzzle (it just goes up and down with the walk), I get the following message:

"The selected frame span(s) cannot be tweened. You must convert frame content to a symbol in order to tween. Do you want to convert and create a tween?"

The muzzle is already a symbol, however. And just to "humor" Animate, I click "OK" after that message, and it converts it to a symbol (a symbol within a symbol, I guess). And two weird things happen:

1. The boundaries for the new symbol are suddenly larger than before.
2. When I create the tween, the muzzle moves side to side instead of up and down-- despite the fact that I never placed a keyframe of the muzzle off to the side!

Any insights?

Answer 1

As a shot in the dark I erased in areas surrounding the symbol. Then I tried the classic tween again and it worked. So the issue was some microscopic mark that was still there. Answered my own question!