Do you have an airgap installed at the sink? Take a look at this
airgap diagram. If there is an airgap, unscrew the top cap and see if it's clogged up. Clean it out and run the dishwasher again. If there is no airgap, check the dishwasher drain hose.
Let us know how it goes. If none of this solves the problem, post back and we'll go from there.