Sorry for the necro, but this has just happened to me. I selected two images in Windows Explorer, right clicked, selected Edit. PDN opens up and I can use the rectangle tool to crop out a small area of one image, but on the second image I cannot use Rectangle or Lasso selection. Magic Wand works so selection itself works, just not Rectangle or Lasso select.
I closed the affected image and reopened it and the selecting tools worked just fine after that.