This one bit me unexpectedly. It's the show-stopping "Licensing for this product has stopped working" dialog in Photoshop CS4, and it seems to affect both Windows and Mac (mine was on Mac)
I found a solution which does not involve dealing with Adobe's tech support (!). Download Adobe’s Licensing Repair tool and run the script.
Adobe CS4 Error 150:30 (license error) – solution
Linear Mode
