Keurig tweaked its machines to ensure that, instead of working with any properly sized pod, they could only work in the presence of special-wavelength infrared ink.
You are probably using a new machine if the cups are not working. Please watch the following video for a quick fix on how to make the cup work with your machine:
Keurig obviously does not want people to use any other brand with their machine. Am sorry for making you take an additional step.
You may need to put a little magnet under the machine. With the magnet, you may not need to cover the top of the cup.
Please watch the following video on where to put the magnet: