When Richard B. Shull's character rips the list of studio phone numbers from the café wall, the list clearly has a nail hole and a tear at the top. When he holds the list against a phone booth window, the hole and the tear have both vanished.
When Tater first escapes the two correspondence school he steals a Model A Ford which soon runs out of gas. The gas gauge shown on 'E' is not from a Model A, which utilized a float window, not an electric gauge.
When Tater is shooting his gun as one of the extras in the rocks, and coming off the hill, he fires his gun eight times. He was only using a six shooter.
Lewis is lost in the desert and rescued by Howard. Howard brings Lewis back to the film studio camp and pass by an outcropping of rocks (which appear in numerous movies and TV shows). The film company eventually packs up and heads on back to LA (this happens during the day). They travel the rest of the day and after dark they again pass by that same outcropping of rocks (they either traveled in circles or instead of traveling back to LA they were stationary most of the day!).
When filming a scene Lewis is punched in the stomach and he doubles over. He is then pushed out of the scene and Kessler yells "Cut!" But the film keeps rolling and Lewis is seen being dragged across the scene. Had the scene been legitimate the filming of the scene would have ended with "Cut!" and Lewis would not have been seen being dragged away (at least not in the black and white version).
While directing the fistfight scene in the desert. The director walks back and forth in front of the camera. Even at one point stopping right in front of the camera. Thereby ruining a lot of the shoot. This may have been meant to show what a bad director he is.
When Tater is laying on his bed in the boarding house, an instrumental version of "I've Got a Feeling You're Foolin'" is playing on his radio. That song hadn't existed yet. It was an original song written for the motion picture 'Broadway Melody of 1936', 3 years after this movie takes place.
In Polo's office there is a poster for the film It Happened Out West (1937) - that wouldn't be released for years.
The road that the old jalopy travels is clearly a modern two-lane-wide paved blacktop, with sand barely covering the lane markers.
The story is taking place in 1933, as per the license plates on the cars, and the date on the letter. Anna Christie with Greta Garbo, advertised with a huge poster as playing at the Carthay Circle Theatre, was a 1930 release, and would have only still been playing its last runs by 1933.