Yesterday, just after replacing my light magenta Epson cartridge for the first time, I tried to resume printing. Instead, I got a Service Error Code 1404. Called Epson tech support, and was told that it is most likely a pressure problem with the new light magenta cartridge. They suggested I go buy a new cartridge, and install it. I am ready to do so, but, I can't open the compartment housing the cartridges. It remains locked, the red ink warning light just keeps blinking. I tried turning the printer off, then on again. I've held down the button that should open the compartment several times for more than the 3 seconds required, and nothing works.

Any suggestions on how to get the compartment door to open so I can change the light magenta cartridge?

just force it open from the left side, it's designed to pop open as a fail safe.

I did as you suggested and it worked. Thanks for the tip.