What is a Spotted background Layer?

[paul_photoshop]

I have managed to do selections from several photos and dragged them onto the same photo, into different layers successfully, with the image being displayed on the layer chequered background. But sometimes when I do this the image can't be seen in the layer thumbnail. All I get is a spotted layerbackground and the image is not displayed, although it can be seen in the workspace. What does this indicate

[KoRniquet]

I'm guessing memory faults ? Are you working on large resolutions? If you are, your computer's hardware might not be able to handle the process of commands in Photoshop. I'm just guessing, though, 'cause I've never seen anything like that before. Hope that helped.

A screenshot would be useful to clarify your question.

Take care,
?D.