I had it too, after adding a new Denon DVD player (timing could have been a coincidence). This was a pain because it moved the "thumbs down" button on my DirecTivo to the second page of the device. I did what was originally offered as a solution above: I went into the customizations and set the value of the "E" button to blank. It went away after my next Update. The original definition that it showed up as set to was something like NumberEnter, which is different from Enter.