Something like this happened to me as well. I filed my N400 along with my husband and son in early december last year. Though, I knew my Green card anniversary was not at the same time as my son and husband, I thought they would consider the case of a family. My application was accepted (I was happy), I got my FP notice, I got my IL notice and my interview was on same day as my son and husband. Their cases got approved without any problem. During my interview, I passed all the questions but towards the end the officer said I have not passed my 5 year anniversary date as yet. He rejected my case and wrote that I can apply after 7/26/2010.
Yes, they took money for the application and raised false hopes but no one can do anything.
So I applied again on 7/28/2010 (waited two more days than whey they said to apply). This time around i did not get a FP notice because I got a letter in mail stating that my old FP is still valid. Now I am waiting for my case to be transferred and to receive interview letter from fairfax, VA office.
Don't know why Fairfax, VA office is taking so much time this time around.