Not sure just what you're referring to, more details please. Are not able to access a web server? A mail server? An online server you've set up through a service like DigitalOcean or AWS? Also, the problem is presumably via WiFi on your Tab but is said server accessible using a different WiFi network, or a cellular connection, or through a wired connection on a PC?
Or is this not necessarily a specific 'server' and that's that just part of the generic error message you're encountering? Have you tried to just power off your Comcast modem/router box and start up again? If there other devices also using this same local network are they also having connectivity issues or is this limited just to your Tab?