Unable to Import Model Error for this one model only

When I use the "Send to Substance 3D Stager" feature in Substance Painter, I get the "Unable to Import Model" error in Stager.  But it gets weirder than that.

Maybe there's something wrong with the model?  Well I can import the model directly into Stager with no problem.  I can also import the model into a fresh scene of Painter, and then use the "Send to Substance 3D Stager" and it works with no problems.

Just to make sure there wasn't something weird going on with my materials, I deleted every layer in my texture set and replaced them all with standard fill layers.  Nothing special.  It still doesn't send.  So there's nothing wrong with the materials.

I have also exported all the textures from my scene, opened a new Painter scene, imported the model, and re-connected all the textures, and when I send it to Stager after doing that, it works.

It's almost like my working SPP file is bugged and just won't send to Stager.  For the record, I have tons of other working Painter files that send to Stager no problem.  It's just this one.  Any ideas what could be causing it?