hello Chanwut
GLOBAL ISSUE ON IOS MOBILE DEVICES WITH GOOGLE APPS
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A Global issue with Google sync is affecting a majority of users accessing their GApps account in iOS.
The affected users are able to access their Google account via web interface, but are seeing error messages and/or other unexpected behavior in mobile devices, especially when they want to synchronize their calendar.
WORKAROUND : use the IOS Google Calendar application instead of the iOS calendar application.