If after a sync you get a notification with the error 'iTunes library couldn't be found' It indicates that Cloud Tuner has failed to fing your iTunes Library.xml on your cloud service. This error has 2 main causes that can be easily solved.
On your computer with your iTunes library ensure that your cloud service has finished syncing and all your files have been uploaded. If you're still encountering an error, check number 2.
If your cloud service has finished syncing but you continue to get a library not found error, please check within iTunes that "Share iTunes Library XML with other applications." is enabled under advanced preferences. More details about how to enable this can be found on Apple's support site: https://support.apple.com/en-au/HT201610