This is a sentence from the home page of Yahoo! Makers. It not only provides a lesson in the need for proofreading, but also demonstrates how errors can make you look foolish:
There are so many ways this went wrong. Did the writer mean “It not only provides”? If so, then she should have completed the correlative conjunction with but also, not and also. Or did the writer mean “It provides”? Then the not is extraneous and the and also is redundant.