P: CS6: Program Error if the background layer is dragged to the "add a mask" icon

In Photoshop CS6 version 13.0.1 if the background layer is dragged to the little "add a mask" icon the program throws up a dialogue box reporting"Could not complete your request because of a program error." This is different to earlier versions where trying the same thing show a little "no entry" icon over the "add a mask" icon.

The error message is confusing and the situation of showing the "no entry" icon as per previous versions needs to be restored.

By the way the same error message shows up on two computers so it is not an error caused by a particular machine (both are Macs).