As far as I know, no, you can not supress this message. It's a system level message that can not be trapped by an error.
It's the equivalent of the message you get on the desktop when the network connection fails.
You can try playing around with the user privilege timeout setting, maybe it will auto-retry and suppress the message for you. See page 21 of the dev guide: http://www.filemaker.com/support/product/docs/12/filemaker-go/fmgo_development.pdf for more details, but it does not cover a network disconnection, which that message represents.