When Robert Blake is facing outside his cell as the men are lined-up, his hands are down. When it cuts to outside the cell, looking in at Blake, both hands are holding the cell bars.
On Lou's first day in prison, the calendar in the conference room starts on a Tuesday but the calendar in the warden's office starts on a Saturday and the calendar in Mickey's office starts on a Wednesday. Coincidentally, the calendars might fit together if the warden had the current month, Mickey had the previous month, and the conference room had the next month, but apart from explaining how that could happen, all three calendars show months with 31 days, so it would not be possible because there are no three consecutive months of 31 days.
In the pre-title sequence, Gannon falls down a stairway with three people standing behind him and a handrail in the middle on which he briefly leans. In the next shot of Gannon continuing his fall, the people and handrail are gone even though you can still see the top of the stairwell.
A sign at the subway entrance in the beginning of the film (and again at the end) misspells Van Cortlandt Park (in the Bronx) as "Van Cortland Park".