Please confirm the information below first.
1. iTunes version is 22.214.171.124 or later.
2. iTunes runs normally, iTunes store can be connected normally, videos/musics/audiobooks can be played by iTunes normally, there is no prompt of expired certificate or session timeout.
3. The prompt box is closed when you convert a unauthorized video, if not, all conversions will fail.
4. The Apple ID you used to sign in iTunes is not locked.
5. The internet connection is fine.
If above are confirmed, please contact us with the following information.
1. Total converted file size.
2. The file names you are converting.
3. Simultaneously converted video quantity.
4. Other operations with the program while conversion.
5. Click top Settings>Help>Bug Report, and submit Bug Report.