To begin the 2nd quarter, B6 replaces B5, but B6 did not report to the scorer's table. Team B takes the floor, and the table hits the horn and calls the official over, notifying him that B6 did not report. Technical foul?

No, you simply bring B5 back into the game.

Correct me if I am wrong, but should this be discovered after the ball is put in play then it would be penelized (by rule, but not typically in practice)???

Trigger, this happen last tues? and if so was it the orange and black or the green and gold that did it?

By rule once the ball becomes live, the substitute become a player, so you can't penalize it.

Paxson-->

It was St. Charles. I was away from the table ready to inbound, and I think this is what happened, but my partner took care of it without asking for assistance.