This particular chapter of Paul's second epistle to the Thessalonians has been the subject of much controversy among those who delve into prophetic truths. More than most it is a that requires skilful rightly dividing of the word of truth, for failure to do so can lead to much confusion and error.
The difficulties of the passage are compounded further by the fact that various translations differ in the rendering of verse two. As Mrs E.Potter, our questioner, rightly points out, the A.V. and NKJV translate it 'Day of Christ' whereas most other versions translate 'Day of the Lord'. This is because the A.V. is based on the Textus Receptus (Received Text) of Erasmus and Beza whereas most other translations use the Nestle Greek translation.