Air in the brake system

Bleed the brake system.

Leaking brake pipe/connection

Locate and fix the brake pipe/connection.

Parking brake switch circuit grounded

Locate and fix the short to ground in the parking brake switch circuit.

Parking brake not released

Release the parking brake lever.

Low brake fluid

Add brake fluid in the master cylinder reservoir.

Leaking caliper piston seal

Replace the caliper piston seal.

Leaking master cylinder (internally)

Repair/replace the master cylinder.

Uneven brake linings

Replace the brake linings.