While showing the monitoring equipment, Hank tells Fred that he could be anyone from Arctor's circle of friends, including Barris. This made sense in the book, however, by this time in the movie Hank has already seen Fred alongside Barris, so he could not possibly think they are the same person.
(at around 5 mins) While Bob/Fred is giving a speech at the NewPath building, he takes his arms off the Podium and turns his side to the crowd. In the next shot, he's facing forward and his hands are on the podium again.
When Luckman first brings in the bike, he lifts the front wheel into the air, holding the bike with both hands on the handle bars. As the scene cuts to a different angle while he is talking, one hand is now on the cross bar with the other still on the handle bars.
(at around 35 mins) During the conversation in the tow truck between Barris and Arctor, visible landmarks switch between Irvine, CA (on the Tustin border) when the camera is on Barris, and Orange, CA (on the border of Anaheim) when the camera is on Arctor. In addition, the same exterior shots from Interstate 5 of the Irvine Technology Center business park are passed several times in the same scene.
(at around 35 mins) After the car breaks down on the freeway, they cut to a scene where the car is facing backwards on a flatbed tow truck. If the car was picked up on the freeway, it would be facing forward unless the tow truck picked up the car from the rear which on the freeway would be highly unlikely.
The goof item below may give away important plot points.
When Fred enters Hank's office wearing the scramble suit, Hank immediately recognizes him and greets him by his name. Although Hank discovers Bob's real name towards the end of the scene, many people that work there wear the same scrambling suit, thus it would be impossible to know who walked through the door.