Does the file play if you right click it in windows explorer and select JRiver MC as the playing device?
Try copying the file, make a duplicate and rename it. Don't delete it, copy it. See what that does.
Also, will it play in other prgrams?
So, it did play in JRiver when right-clicking in File Explorer. However, the same failed in VLC.
I did a little experimentation and renamed the file to something shorter, and lo and behold, JRiver successfully imported it. So, despite the longer file name support being enabled, it turns out JRiver still chokes on files with longer names. At least this one.
Quickly trying to guess at what the magic file length is, the full file path that JRiver objected to was 260 chars, while the shortened length that successfully imported was 214. So, I'm guessing it's going to be 255 (or 256) characters.
In any event, it would be much appreciated if JRiver could provide a meaningful error message in the results window when this sort of thing happens. Just failing without explanation is suboptimal. :-)