This error results from a limitation of the iOS system process that serves iTunes Music Library tracks to third-party apps like Go Button.
iOS does not give Go Button direct access to the audio files in your iTunes Music Library -- that only happens for the files that you import into Go Button's "Documents" folder. So, if your show uses a large number of tracks from the Music Library, the iOS service that provides these tracks to Go Button can become overwhelmed when you first open a show. When this happens, those cues will appear disabled and display a "too many files open" error message.
The actual number of Music Library tracks that can be accessed at one time varies from device to device, depending on its specific capabilities.
To avoid this problem, we strongly recommend that you import your audio files into Go Button using one of the many methods described in Working With Audio. You can then find your audio in the "Documents" tab of the Media Picker and assign one of those files to your cue or hit.
Having your audio files saved in your Documents folder is not only more efficient for Go Button to access, it also allows you to include your audio files with your show data when you export it as a show bundle.
Apple added a new security measure in iOS 10 and newer which requires your consent before an app can access your Music Library. Until permission is, any cue or hit that tries to use a Music library track will appear broken, even if the track is synced to your device and can be played in the built-in "Music" app.
You can manually enable this permission in the iOS Settings app by navigating to Settings > Privacy > Media Library, or on Settings > Privacy > Media & Apple Music on newer versions of iOS. Enable the switch next to "Go Button", and you should be all set.
We have discovered that the Google Drive sharing extension currently appears to strip some very important metadata attributes when it uploads files. When this happens to .gobutton and .gobundle files, Go Button is no longer able to recognize that those files are compatible. This is why they appear grayed-out the next time you attempt to reimport them from Drive.
We recommend uploading to another cloud service like iCloud Drive or Dropbox if you can. So far, we have only seen this problem with uploads to Google Drive. Other developers have reported the same problem with Drive whenever trying to upload files that have a non-standard file extension, and we have verified this same behavior happens in other apps besides Go Button.
If you do need to use Google Drive, a workaround is to select the "Copy to Drive" option when you are exporting your show from Go Button (instead of tapping the "Google Drive" icon in the sharing menu). You may need to scroll the row of sharing icons to the left in order to see "Copy to Drive". This option might also be behind the "More" button. Choosing "Copy to Drive" copies your Go Button document directly into Drive, which bypasses the sharing extension bug. Files transferred into Drive this way will retain all of the correct attributes and won't be grayed-out when you want to import them on your other devices.