Error when importing Substance archive into Unity 5

Most of the time, .sbsar files import into Unity flawlessly. Occasionally, I'll come across a file w$$anonymous$$ch will not import successfully into Unity. All the files I am trying to import are authored by me, using the Mac version of Substance Designer 5. When the arc$$anonymous$$ve doesn't import correctly, I get the following error:

Failed to retrieve a single SBASM file in the arc$$anonymous$$ve... Did you use the Substance cooker to generate the arc$$anonymous$$ve?

I have of course tried the usual t$$anonymous$$ngs: restarting both programs several times, exporting the file from Substance under different names with different settings to different directories, etc., and not$$anonymous$$ng has worked. Most of my substances do work, but I have two so far that refuse to. If it is of any importance, the two w$$anonymous$$ch I am having problems with have substantially more complicated node graphs generating them. The strangest t$$anonymous$$ng is that w$$anonymous$$le they won't open in Unity, the arc$$anonymous$$ves open and generate fine in Substance Designer.