Profootballtalk.com has published their take on what they think might have happened regarding the disapproval of the Shaun Rogers trade between the Bengals and Lions.  The piece is worth a read, both for the swipe that Bengals P.R. director Jack Brennan takes at the team's website and for additional knowledge about how the salary cap works.  Their best guess is that the sticking point had something to do with the $1 million roster bonus owed to Rogers, and whose responsibility that would be.

The last paragraph of the post is very telling, however:

"...if we’re right, we can understand why the Lions and the Bengals are being vague about the reason for the failure of the trade.  It essentially means that neither front office understood a basic concept such as the moment at which responsibility for a roster bonus cannot be avoided.  And candor in this regard likely would have led to the same kind of embarrassment that dogged the Vikings after bumbling their first-round picks in two consecutive drafts."

I find this characterization extremely unfair...to the Vikings.  The Bengals' front office has been "bumbling" first round picks and displaying embarrassing incompetence for years.

(NOTE: I personally think this will end up working in the Bengals' favor.  As I stated in comments earlier today, I don't think the team needed to take on the baggage that Rogers brings (creaky knees, run-ins with the law, fluctuating weight, taking plays off, etc.), and the Detroit fans don't exactly seem to be upset in letting him go.  It's just another example, however, of how the Bengals simply do not understand how the 21st century NFL works.)