Here are a couple of websites that explain how to measure shank size of your machine and shank size of the foot you have, to see if you have the wrong foot for the machine:
http://www.ebay.com/gds/How-to-Deter...4900176/g.html
http://www.anniescatalog.com/pages/which_foot.html
http://www.thesewbox.com/2008/04/how...hank-size.html