Cannot make a new blog entry

I am trying to make a blog entry and cannot figure out what is not being accepted. I receive the following error:

Your HTML is not well-formed - the entity you tried to use is not accepted.

Any thoughts on how to find the culprit? I did not use c.l.a.s.s. or s.t.y.l.e. in the entry I'm trying to submit... 

Do you have any images or links copied and pasted from another place?LTomlinson21

Well, it took me awhile, but the word that gave me trouble was "e.l.s.e.'.s.", as in, "That camera bag is someone e.l.s.e.'.s."

Thanks!