That is the error one of our clients gets when they try to run GoToAssist on their machine. We have tried making sure the site is not restricted by the browser, but we still get this error.
It looks like you are connected to a Windows XP client, is that correct? GoToAssist Remote Support v4.6 is the last version that may run on a Windows XP PC, a fully updated Windows 7 is the current minimum requirement. From the error you are getting I would suspect it is due to XP not supporting the required TLS versions: enable TLS 1.1. and TLS 1.2