Plot hole: At the end of the episode McCoy and his team tape a conversation between Melissa Corbin and her mother Lorraine in order to record her admitting to murdering Alan, her first husband. Trouble is, she says nothing incriminating. The closest they get is Lorraine asking her why she killed Alan, and she replies "You didn't have to sleep with him." That means nothing, and in fact Lorraine says absolutely nothing of any legal significance during the entire conversation.
Plot hole: Ashley says she is 9; later in that season, in "Just Infatuation," Phil says she is almost 12. Will is 17 for the first two seasons, and 18 in season three. Nicky Banks grows from baby to preschooler between seasons four and five (though this was humorously addressed).
Plot hole: In the bait and switch section, why does anyone involved agree to Leland being Ben's attorney when both victims are relatives of Leland? Neither Ben nor any of the police are in on Cooper's plan, and it seems implausible at best that they would agree to this.
The End of the World as We Know It - S9-E23
Plot hole: Noah cancels the club's scheduled Monica concert because Dylan pays him to have her give a private performance to Dylan and Gina instead. He seems really excited and proud of himself for some reason. Even if Dylan paid him much more than he would have received from the gate (which is likely), this could cost Noah money in the long run. Many customers would probably get angry and decide to stop frequenting a place that would cancel a concert at the last minute for no good reason. Then again, Noah was never exactly a genius - in business or otherwise.