Blender turns off randomly with single serve cup

I have BL642-30 blender and it's just stop blending almost immediately and the light blinks red as if it's not locked in place with the cup. The pitcher seems to has no issue. Sometime I can kind of get it to work if I push down on the cup. I have tried buying a new cup and blades but it's still happening. I haven't been able to find a fix for this so hopefully someone could help me with this.