What is the black and white square in the lower right corner?

[petebale]

Please tell me!

[c.pfaffenbichler]

Could you please post an unclipped screenshot with the pertinent Panels (Toolbar, Layers, Options Bar, …) visible? 

[Paari_GD]

i think there is an single pen anchor point somewhere

please check the path window...

i have attached screenshots to refer

  

i hope it helps..

[melissapiccone]

Where is it? Is this outside of your canvas? We need to see your whole PS window.