I uploaded the c 74 (and when I did, it gave me a message that my current c 74 was newer than the upload, but I did it anyway) and it didn't fix the problem, but...I think I had a couple corrupted song files, as I was able to print other songs, just not the two I had been working on. So I think somehow the two files became corrupted or I did something stupid, and in any event, it looks like I'm up and running again.

Thanks folks!