full article here:An ongoing issue with Adobe Photoshop CS5 that a few people are experiencing is the menu items will not work and instead will appear greyed out after a while of using the program. In some instances only a subset of menu options will be inactive, but in other instances the full menu set will not work.
The problem seems to be intermittent for most people, and happens randomly after using the program for a specific amount of time. Some have reported that it seems to happen after performing specific functions like saving, but for others the problem so far has not been associated with any specific cue.
Unfortunately there are no lasting fixes for this problem, and currently people have only had success by saving their work and relaunching the program or the whole CS5 suite if other CS applicaitons are open. According to Adobe employee "Chris Cox" in a recent forum posting, the problem seems to be with how Photoshop handles system events in Apple's Cocoa API, which essentially means the problem is with how Photoshop is handling input from mice, keyboards, tablets, and other devices.