After upgrading my Android system software from CM 11 (KitKat 4.4) to CM 12 (5.0 Lollipop, I started getting Unknown issue with Google Play Services error message on the notification bar every time I tried to sync Gmail. On Gmail, it would just say getting your messages followed by the error messages. The message would also pop up at random times like when I am updating or downloading an app from Google Play Store. This Google Play Services error seems to affect only Custom ROMs on rooted Android smartphones. There is a very simple way to fix it. Here are the solution for with this “Unknown†Google Play Services error on Android phones and tablets running Cyanogenmod and other custom ROMS: