Sounds like you might need a new master cylinder or have some other problems with your brake system. I assume you have checked the level of brake fluid in the master cylinder, but when is the last time the fluid was changed (should be every two years). The description below is from the Holden VS Service Manual, but I believe the last section is similar for the VR. Having said that, I'm surprised that the error stops the car from starting.
Master Cylinder Construction (VS)
"The tandem master cylinder arrangement provides separate hydraulic circuits for the application of the brakes, in a front to rear split arrangement. Both of these circuits are fed by separate fluid feed and compensating ports, through a common fluid reservoir, that is sealed by a diaphragm fitted inside the reservoir cover. Provision of this diaphragm provides an effective seal against the moisture in the atmosphere coming into contact with the hygroscopic brake fluid, thereby maintaining the brake fluid's design boiling point, for a maximum period of time......."
"In all vehicles except Utility, a proportioning valve is located in a parallel bore in the same casting. This valve is used to maintain the front to rear hydraulic pressure balance and, should one of the two separate systems fail, a separate piston and differential switch (brake warning lamp switch) are incorporated into the design, so that the vehicle operator can be warned of a system malfunction."