Length is but a symptom of an actual problem with a post. Short posts are not bad, for instance, but oftentimes they miss critical details that make definitively answering a post extremely difficult. It's not that short is bad; it's a symptom.
Likewise, posts that are long may not be bad simply because they're long. Yet, posts that are long are more likely to lack the focus that accompanies conciseness and brevity. Long posts sometimes tend to be long because they contain unnecessary information, or because they contain more than one problem.
For there to be excellent Q&A, there must be focus on a single, answerable problem; any of the above reasons for the long post symptom are reasons that make it difficult to objectively and definitively answer a question.
In the example you linked to, it's clear the asker hasn't narrowed down the problem. This person posts several walls of code and expects the community to narrow it down. Good Q&A involves work from both parties, not just the answerers, but also the asker.
Thus, this is an example of a post that lacks focus due to it's length. The poster posted "all of the code" in hopes that someone will replicate the exact environment and solve all of the problems.
I suggest closing this post as too localized, since it's so specific to this person's situation and unlikely to be helpful to future visitors. However, if the asker narrows down the problem, I suggest reviewing it as a possible candidate to be reopened.