DIAGNOSIS The single-serve cup is not engaging with the locking mechanism on the base. This is usually an alignment or accessory issue.
FIX 1. Ensure you are using the correct cup: the To-Go Cup for the SS151 model has a specific blade base with locking tabs. 2. Place the cup onto the motor base. 3. Align the cup's handle with the 'unlock' symbol on the base. 4. Firmly press down and rotate the cup clockwise until the handle aligns with the 'lock' symbol. You must press down while rotating to engage the lock.
IF THAT DIDN'T WORK The plastic locking lugs on the bottom of the cup's blade base may be worn or broken. Inspect them. Also, ensure the rubber gasket on the cup's blade base is present and not overly compressed, as this can prevent proper seating.
HEADS UP The single-serve cup has a maximum fill line (typically 20oz for liquid). Exceeding this can prevent proper locking and cause leaks. The cup will not operate if it is not fully rotated to the locked position.