Factual error: The whole Bowfinger scenario is impossible. They are using a 35mm Panavision cine camera which cannot be focused through the lens; it needs precise measurements on the set in order to be properly in register. Then there are the light readings required to ensure proper exposure. Wouldn't Kit Ramsay notice the man with the light meter, or the one with the tape recorder? Both measurements would have to be done with him or an identically dressed and made up stand-in (a "lighting double") on the spot. Then there is the sound. Any sound recordist worth his salary will have the microphone within centimetres of his subject, and he'll have a boom operator keeping in there. We don't even see a microphone in use! Please don't tell me this is based on the clandestine filming of Mary Pickford during her Russian visit: that was done with old black and white film which has very wide tolerance to exposure and most of all it was silent, and she was aware of the camera crew, she just thought they were news crews. (And the results were rubbish anyway).
Factual error: Daisy is an out of work jobbing actress but she has a credit card that will take the cost of developing and printing the stock used to shoot a feature film in 35mm! Since they are watching colour rushes with synchronised sound on film (not cheaper video) they are not doing this on the cheap, either. Minimum cost, for a 90 minute feature, allowing four takes of each shot (which we see them do) - £41,000.00 or around US$85,000.00. That's some credit card. Anyone got the name of the issuing company?
Continuity mistake: In the scene where Daisy is supposed to meet Bobby at his place, when Bobby empties out his box of money and sets it down, there's a dollar bill still inside of it. The doorbell rings, there's a shot of the door, then a shot of Bobby sitting next to the box and now the dollar bill has disappeared.
Audio problem: When the premiere of "Chubby Rain" starts there is a shot from the back of the audience and you can hear a lot of screaming and clapping, and yet you cannot see anyone's hands moving. However at the end we see a very similar shot, with clapping again and you can see they are doing it this time. Clearly someone forgot to tell the extras in the first shot so they put the sound on afterwards.