All of a sudden, my Epson R2400 stopped printing photoshop CS5 files. It prints files from other programs (apperture, mail, web) just fine. The cartridge goes back and forth and the paper advances, but no ink is applied.
That means that information is going from Photoshop to the printer driver, but something has gone wrong after the image data leaves Photoshop.
You can try resetting Photoshop's preferences (just in case some stale information is stuck in the printer setup).
But after that, you'll need to talk to Epson to diagnose what is going wrong in the OS or driver parts of the print process.