This article contains information regarding getting an "E" error on an MSR

Some customers have reported receiving an "E" (error) when using the Magnetic Stripe Reader, please see information below for possible reasons.

The “E” indicates a bad read for the track (the “E” indicates an error). This would be bracketed by the start and end sentinel for the given track. A bad track 1 read will be “%E?” and a bad track 2 read will be “;E?”.

These errors can be due to a bad/damaged track on the card, a poor swipe, or a dirty or damaged read head. Commonly, the error is due to poor swipe mechanics. Examples of this are swiping the card too slowly or lifting up the card during the swipe.

Dirty or damaged read heads are quite rare and generally result in uniformly (nearly all) bad swipes and errors on both tracks.

Ergonomics can play a big role in bad read events. If the reader is mounted in a manner that makes it awkward for the user to swipe the card smoothly, or if the reader is mounted in a way that may impede the smooth swipe, you will see an uptick in the number of bad read events. Also, some cards may have poor encoding and sometimes these cards read better when swiped in the opposite direction (ex: right to left instead of left to right). So if you encounter an error, try swiping the card in the opposite direction.

Check out a video devoted to swipe mechanics
https://www.youtube.com/watch?v=OhIuQUgjT70