This video explains that the use of the word 'Easter' was not an oversight by the KJB translators. They rejected the word 'passover' found in the Geneva Bible of 1560.
Thus, their use of Easter was a conscious one based on their extensive knowledge of scripture and the English language.
There are no errors in the KJB.
Will Kinney has an excellent article on the subject

http://brandplucked.webs.com/easterreplenish.htm