I consistently have a similar problem. For whatever reason, I can't post any decent amount of text, and it only goes through once I've cut it down to an occasionally ridiculous length. By ridiculous, I mean about a page of size 12 on MS Word. Mind you, this isn't always the case, which confounds me even further.
I assume this error is temporary, but if you must post now, just cut the chapter into a few pieces (or perhaps many, many pieces) and post them separately.