Yeah, this one's common. You're using the wrong soap.
FIX: Only use detergents specifically designed for dishwashers. Regular dish soap or laundry detergent will absolutely cause it to fill with suds. Stop the cycle, scoop out as much suds as you can with a cup, and let it settle.
IF THAT DIDN'T WORK: If you are using dishwasher detergent, you might be using way too much. Check the manufacturer's recommended amount. Also, rinse agents like Cascade Platinum Power Dry or Finish Jet-Dry are designed to prevent film and spots, but they won't cause sudsing.
HEADS UP: Keep all detergents and rinse agents out of reach of children.