The "Ink Waste Pad Saturated" message on the Epson CX7800 means the printer's internal waste ink counter has reached its limit. To resolve it, you'll typically need to reset the waste ink counter using a compatible Epson reset utility or service tool. Keep in mind that simply resetting the counter without servicing or replacing the waste ink pads can lead to ink overflow in the future.
If you're seeing Error E91, please share the exact message and your operating system, and someone may be able to recommend the correct reset tool for your printer model.