I've seen this on some Android devices that prevent apps from writing to the extra SD card even if the app has been granted the right permissions.
In this case, the app wants to rename your files to add the record ID to the filename, because that's how it names files when it downloads them. It will still read the files if they're there without the ID, but when you attach a recording, it tries at that point to rename the file.
If you need to use the SD card, you could turn off Settings > Account Sync > Auto-Download Files, then add the recordings to the song on your computer. Then BandHelper will know the song has recordings, and will read them off the SD card, without trying to rename them.
Or if you have space on your internal storage, you could change the download directory back to the default and everything should work normally.