When you import content from Dropbox using OnSong, the files that appear within OnSong are listed from the Dropbox web service. If you are not seeing the file listed, it's likely that the file was not uploaded to the Dropbox cloud storage. You can view what is located in your Dropbox cloud storage by visiting http://dropbox.com/ and signing in with your Dropbox credentials.
If Dropbox does not contain your file, it's likely that the file has not yet been synchronized from your computer or another app running Dropbox software. This can happen due to a network outage, network security settings, or an issue with the app that is installed on your computer. For instance, if you drag a file into a Dropbox folder on your Mac or PC, it may take some time before the Dropbox app uploads that file to the Dropbox cloud. If the file is large, it can take longer. Another common problem happens if the Dropbox app has stopped running in the background on your device.
If you've recently installed a Windows or Mac update, be sure that any update process or change in your computing environment has not caused the Dropbox app to stop running or functioning correctly. Be sure to install any updates to the Dropbox application and contact Dropbox if you need assistance.
Also, be sure that you are running the latest OnSong update to ensure any changes made for compatibility with Dropbox may not be affecting your workflow.