At the begining of the film, there are articles hanging on the wall talking about Michael Myers and his infamous killing sprees. One of them says "Laurie Strode, who survived the Haddonfield murders in 1968...". The year should be 1978, not 1968.
There is also picture of Laurie Strode's graduation day shown in the newspaper clippings. It says "Class of 1978". This is wrong, because in the film Halloween, the month is obviously October, and we are told Laurie is in her senior year. Which means she won't graduate until summer in the next year, 1979.
Refrigerator on Battery Backup?
In the beginning, when the nurse sees someone has come in her house, she goes next door to get help. The kid decides to go in and check it out himself. Notice that as soon as he enters the house, he tries to turn on the lights, but can't - no electricity. He then moves on to the kitchen where he opens the refridgerator door. The light comes on!
Miscalculation in Sister's Age
When Laurie is confessing to Will who she is, she mentions that Michael murdered Judith (first sister) when she was 17. However, when Michael places the tombstone over Annie in Halloween, it reveals Judith was born November 10, 1947. Considering she was killed on Halloween in 1963, she would have actually been 15, not 17.
Was That Head or Feet First?
When John and Molly are running out of the building, John jumps out of the window head first, but when the camera cuts back to him, he is seen coming out feet first.