Other mistake: When Peter calls the lab about Kyle's sperm count results, the camera closes in on a blue folder with Kyle's name on the label. Yet the lab tech picks up a pink folder and reads the results.
Divorce Dominican Style - S7-E1
Other mistake: After Taylor calls Michael from her truck to tell him goodbye, she then starts the engine and the camera pans to the exterior of the truck, showing a long green hose that extends into the front cab, gushing carbon monoxide, when there was no sign of the hose around the truck beforehand. And seriously doubtful that she rigged the hose herself, in her pregnant condition.
The Night the Lights Went Out at Melrose - S7-E13
Other mistake: The whole city is purportedly in a black out, but porch lights remain on during every scene in Melrose.
Other mistake: After Brooke blackmails Amanda for the position of company vice president (over Amanda's affairs) Amanda gives in and calls a short conference with Alison, Brooke, and Billy, and openly demotes Alison to 'assistant'. Which is impossible, considering Alison is the company vice-president. And only a higher ranking head could call such a shot, while Amanda is an accounts executive with no such power or authority to overthrow anyone above her.
Other mistake: Jake Hansen (Grant Show) wears a gold wedding band on his left or hand during the shows run, when he's supposedly single.
Suggested correction: Not really a mistake, just a character choice. Grant Show wasn't married at the time, so it's not his wedding band we see, it's just a ring.