The E means that there was a large discrepancy between at least two of his scores, by more than 20 pts.. The N+ means his strength was in the Nonverbal. Follow this link which the score was plugged in and it will give you more specific information.
http://www.riversidepublishing.com/products/group/cogat6/results.jsp

Sometimes they can represent an underlying disability or learning difficulty that warrants further investigation. Other times, it doesn't mean anything in particular, but it's worth lookin into. One think to keep in mind is that in 3rd grade the CogAT is no longer read to them, it is read by the child. Schools tend to think the scores starting at 3rd gr. are more reliable than early scores because of the fact that it is done by the student, not someone reading the questions to them. If you state that he has difficulty in reading already, that would probably explain the discrepancy. I would look into it to see if there is an underlying reason that may be causing him difficulty with reading and spelling etc. HTH!