Can someone translate this into plain english?

It means that on line 116 of that doent there was an illegal character, that is, a character that is not legal in HTML. If you open the doent and scroll down to line 116, it should be obvious -- the illegal character will be a copyright symbol that someone put in as an actual copyright symbol, which is not legal HTML. Change it to " & c o p y ; " (without the spaces!) which is the legal HTML entity code for a copyright symbol.