Original post by: Robert ,
Here's the problem and the solution (on my 2012 MacBook Pro): I had this issue and found that pressing down hard on the E key before the problem keys or the lower case to the right of the trackpad got it working again for a bit sometimes. It also worked fine using a USB keyboard. took it to a repair place and they got it working for a couple weeks but then the problem returned. What the real issue turned out to be was the battery was swollen after two years. If you have this problem, remove the battery and run the computer from the power cord only and see if the problem goes away. In my case it did, so I ordered a new battery and installed it, and with a new (unswollen) battery, the problem didn't return and the computer works just fine. I didn't change the keyboard or the top case, just the battery. No more issue.