I ran my epub through the 1.0.5 validation tool. Looks like I'm getting errors based on my HTML.
I received two types of reoccuring errors.
ERROR: c:\test.epub/nexus_ascension_split_019.html(8): bad value for attribute "id"
ERROR: c:\test.epub/nexus_ascension_split_018.html(53): element "br" from namespace "http://www.w3.org/1999/xhtml" not allowed in this context