Appointments+: Error refreshing the OAuth2 token message: '{ "error" : "invalid_

I'm using 1.2.8 of Appointments+.

While using 'Test Connection' I can see an error in the logs:
[May 19, 2013 1:49 pm] Error refreshing the OAuth2 token, message: '{
"error" : "invalid_grant"
[May 19, 2013 1:49 pm] Error calling POST (401) Invalid Credentials

The plug-in was working for me locally but cannot get working on hosted server. I have deleted and reinstalled plug-in and attempted setup from the beginning three times, following the video as well.

The timestamp of the log message is about 30 minutes ahead of my local time. I confirmed the Google calendar and WordPress setting for timezone were both set to the same (Central - US / Chicago).

Please help me debug, thanks.