When the doctor (Vic Perrin) asks Barney what kind of current will there be (at the mission briefing), Barney replied "Direct, but the voltage can vary so I'll bring along some rectifiers to compensate". But rectifiers don't compensate for voltage changes, they change alternating to direct current. Also voltages are different around the world, but they are all alternating current.
When Cinnamon arrives at the gate for the party, it's supposed to be night. However, over the guard's shoulder is light blue sky.
When Barney shoots the book with the metal plates inserted to demonstrate the bullet won't penetrate, the toolbox doesn't move. The impact of the bullet would still have been transferred to the toolbox. Unless the toolbox was filled with lead, a shot from that close should still have moved the toolbox and the book at least some distance across the table.
The ceiling view in the padded cell reveals 3 shadows of the hanging lamp suggesting 3 spotlights aimed up at it.
In Mission Impossible, vehicles in scenes set in foreign countries are fitted with fake number plates (often of exactly the same design, regardless of the fictional country being featured), but unusually in this episode the taxi which appears in two scenes (actually a Beardmore Mk7 Paramount from the UK, built between 1954 and 1966) still has its original UK registration number in addition to the filmmakers' fake plates.
When Rollin is applying the "Wilson" disguise to Dan, the individual appliances have thick, square-cut edges. These would never blend into a believable mask. Actual makeup appliances taper down to delicate, wafer-thin edges.
When Barney & Willy are removing the unconscious envoy from the trunk of the car you can see the 'unconscious' envoy's hand start to grab the lip of the trunk opening.