Other mistake: Towards the end where they steal the chip, they are detected and about a million security guards are all running around, yet 30 seconds later, the ONLY security guard is ONE MAN with a shotgun. What happened to their big army of security guards?
Continuity mistake: When Whistler is driving the van, he hits the two cars and knocks out the driver's side headlight, yet right after this and through the rest of the film, the headlight works properly.
Factual error: In the scene where Redford's character enters through the secured entrance with the stolen key-card, it shows a printer printing the time he entered. Then after his walking and getting up to the top floor and trying to get past the voice verification system and having to do it twice, they show the same printer printing the time he passed that checkpoint, and it was only one minute later than the previous time. Even though seconds are not shown, all of these actions must surely have taken longer than 1 minute and 59 seconds.
Plot hole: At one point in the movie they go through a lot of effort to prevent a phone call to Mr. Abbot from being traced. The computer screen shows that the call was hung up before it could be traced, yet at the end Mr. Abbot manages to find them back at that same location. Also, Redford's character declares that location to be not safe anymore in the middle of the film, so it's puzzling as to why they would even return there after they recovered the box from Cosmo.
Continuity mistake: When Robert Redford tips the scrabble letters onto the glass table, he makes "SETE" and "CAST" next to it. To the right of "CAST", under his right hand, are the letters RNY, quite widely spaced. All other letters are tightly gathered above. When the angle changes to under the table, suddenly all the letters are spread fairly evenly around the table.