A breaker will trip when Hot is connected to Neutral or Ground without first flowing through a load (short circuit). If the issue occurs when the switch is turned on, then the wire connected to the Red load screw is connected to Neutral, not the Load.
If a GFCI outlet or circuit breaker is tripping, it is typically because the Neutral connection on the switch is tied to Ground. This is a safety hazard and violation of National Electrical Code. If you are unsure please contact an electrician. Please note, shorting the output of a dimmer will probably cause permanent damage to the dimming circuit.