How can I get rid of the "Choose Application" window that sometimes appears in OS X? An example: When I open Photoshop I get a window asking "Where is Photoshop?" It then tells me to choose the applications from the list of applications on my mac. Meanwhile, Photoshop is open and working fine.

This happens on a dozen or so programs and I don't have a clue why. I've searched online but to no avail.