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In FileMaker Go, tap the wrench icon in the upper right corner. Make sure Auto-Restore Login is turned ON.
In FileMaker Pro, pull down the File menu and select Manage -> Secuirty... Make sure the account belongs to a privilege set that has the extended privilege "fmrestorelogin".
Also in FileMaker Pro, pull down the File menu and select File Options. Make sure the user name and password matches what is being used to access the file.
For more information about fmrestorelogin, please see page 11 of the FileMaker Go Development Guide at: