Crew or equipment visible: When Nancy, Ned and Corky peer into the newly discovered secret passage from the attic, a spotlight is visible hanging behind them. It is also included in the ink drawing of that shot in the credits.
Incorrectly regarded as goofs: When Nancy spends her first night at the home in Hollywood, there is a digital clock/radio on her bedroom nightstand. In the next scene, it has been replaced by a old-fashioned wind-up alarm clock, which awakens her. Nancy mentioned she likes old-fashioned things. It is possible she took the alarm-clock which had been there and replaced it with her own.
Factual errors: The sign outside the church in the opening sequence appears to say "Calvary Presbyterian," and Nancy refers to "the pastor," which is consistent with a Protestant church. However, in the sanctuary, there is religious statuary, and Nancy disguises herself as a statue of the Blessed Virgin (with an amazingly handy bit of fabric in the traditional blue which always adorns Mary in traditional religious art). Presbyterians come from a strict Calvinist tradition that eschews statuary as idolatry, and they don't pray to Mary.
Continuity: When Nancy is talking to Ned on her porch, her yellow hat ties in the back in the over the shoulder shots, but near the front in other shots.
Factual errors: Nancy Drew says the Miranda Warning started in 1963. It was actually the result of a ruling in June 1966.
Continuity: After Nancy gives the blondie to the hospital worker, he calls her back to give her the information she needs. The shots facing Nancy show the napkin empty without the blondie on it. The shots facing the hospital worker show the blondie returned in the same spot again.
Revealing mistakes: When Nancy is printing out the details of all the possible matches on the 3 adopted children; although the names in the left column of the pages are different, the list of addresses in the right column is the same on each sheet.
Factual errors: The train Nancy and her father travel to California in is clearly marked as a "Coach" car. The coach class train cars on the Amtrak California line do not actually include beds.
Factual errors: During the chase scene between Nancy Drew's Nash convertible "roadster" and the bad guys' Range Rover (starting at 1:20:20 on DVD), the Range Rover bumps the Nash three times. Nancy Drew's head snaps forward when physics would dictate that her head would first snap backwards (i.e. whiplash).