1994 968 Clutch won't disengage

Vehicle Information: Model(924/944/968): 968; Year: 1994; Body Type: Coupe; Total Mileage: 63,000;

After the car has been parked on an incline (slight up or down hill) without using the ebrake. When I depress the clutch it does not disengage and I cannot move the gear lever. The car will start but turns over slowly, then the clutch releases and the car will roll back and I can move the gear lever. Otherwise, the clutch works normally.