Comment 33 for bug 737615

The problem is in the settings of the connection, but unfortunates the manager does not display this information.

SOLUTION:
- start nm-connection-editor from the terminal (sudo is possible, bus probably not necessary).
- open the connection settings as usual in the popped-up manager
- The exact error message will be printed in the terminal, read it.
- Fix the error and the buttons will be available again.

EXAMPLE OUTPUT in the terminal (in German in my case and I had to mark Certificate as ignored ):

** Message: Cannot save connection due to error: Editors wird initialisiert …
** Message: Cannot save connection due to error: ungültige Einstellung Sicherheit des Funknetzwerks: Ungültiges EAP-PEAP-CA-Zertifikat: Kein Zertifikat angegeben
** Message: Cannot save connection due to error: ungültige Einstellung IPv4-Einstellungen: ipv4.addresses: Diese Eigenschaft darf nicht für »method=manual« leer sein