blender won't lock onto base

My Ninja blender won't lock onto the bottom of the base. It usually sits straight down on base with corners unmatched then you turn it a quarter of a turn to lock it in place. It won't even sit on the base straight down. It has no broken pieces or any particles of anything in the way to keep it from lining up. I usually use the small cup for everything, but I need the big blender today. Did I forget about some safety feature or something?