When using the Universal Lid, rim of container should be smooth and flat. Ragged edges will prevent lid from vacuuming properly. Make sure rubber gasket underneath lids as well as rim of canisters or containers is free from food materials. Check knob on lid to see if it is closing and opening properly and that there are no food materials caught inside. Make sure Accessory Hose is securely inserted into Accessory Port on appliance and in port on accessory lid. Make sure knob on accessory lid is set to Vacuum. (If your accessory lid has a knob, make sure the knob is set to Vacuum.)