4.1 jelly bean - Network Error when invoking Google Now

When I try to invoke Google Now by swiping up from the Home button, I get the message "Network error. Check your network connections and try again". I have a solid WiFi signal, and searches from the search bar work fine. I get the same message when I go into settings after launching Google Search and try to enable Google Now.

ASUS Transformer Prime, Android 4.1.1

Answer

Finally found the answer. I had four Google accounts - one of them could not sync because it required domain policy to be enforced, and I hadn't allowed that. I connected the tablet to my laptop and used adb logcat to see what was being logged when the error was displayed:

I/GLSUser (28125): GLS error: DeviceManagementRequiredOrSyncDisabled <> oauth2:https://www.googleapis.com/auth/personal_derived_data https://www.googleapis.com/auth/paths.notifications
V/GoogleLoginService(28125): Returning error intent with: ComponentInfo{com.google.android.gsf.login/com.google.android.gsf.login.LoginActivity}
E/Velvet.VelvetNetworkClient( 4564): Failed to get auth token

(these messages were repeated several times).

I guessed that the errant account may have been involved (even though it was not the account I was trying to active Now with), removed the account from the device and all is well.