error during simulation

Hi

I am simulating my project using Quartus II and getting following error

Error: Simulation results from c:/altera/80copy2/quartus/voq_switch/db/voq_switch.sim.cvwf (0 ps to 1.0 us) do not match expected results from vector source file c:/altera/80copy2/quartus/voq_switch/voq_switch.vwf

can u please tell me what could be the problem

Thank you