ok, ran into the same problem, I think I found a solution.

first, embed all your links. then unembed all the links, NOT to the original location, but to a new location. so create a new folder for all the linked files. after you have copied all the files into that folder, you can check for any files that have “/” in their names.

I did this and sure enough, found this one file with “/” in its name. I didn’t bother to try to package again with the same file name just to see if the reason for the problem is indeed the “/”. I just changed the file name and the package was done without any problem.