I posted this reply to your reply on my thread. Double-posting here for discoverability for others.
TLDR: Don't use WordPress with MSSQL.
Original thread with the kind of issues you'll see: http://wordpress.org/support/topic/sql-server-query-errors-for-search
I dug into the MSSQL plugin and it turns out that it's a complete hack. Maybe it's the only way to support MSSQL, but the solution is to perform just-in-time string manipulation to translate the MySQL query to the MSSQL syntax. As a result, it's extremely brittle and very risky to take a dependency on.
I wouldn't recommend anyone use it because you can't rely on WordPress updates (as they might break the translation layer since they don't QA for it). You also can't rely on plugins since they don't build or QA for it. This isn't really anyone's fault, but just a fact-of-life for software. In my case, I dug into the WordPress changelog to track down the specific error I was getting in search to a seemingly innocuous change to order the results by relevance in title before body. There was no quick & easy fix, so I simply short-circuited the logic to not do that. I have other errors that happen occasionally, but my pet project site isn't worth the effort to address them at this time.
To be clear, WordPress is awesome and MSSQL is awesome. However, WordPress on MSSQL is a bad choice because WordPress was not built to be DB-agnostic. Maybe someday that will change, but it'll still take a long time for plugin vendors to migrate forward as well, and I doubt most will. I completely regret taking the Brandoo path. You should get off it as soon as possible.