I just got a letter is in blue paper. It says that it is a Finger print Receipt Notification (This is not a bill). The application number does not work in uscis.gov, it also says that We have collected the fees for Fingerprint fee and I-751. There is no date when to take the fingerprint. Has anyone got a such letter? I am suspecting it is a receipt just saying that they have cased my check.

Yes it is just a reciept.... you will get the appointment letter in the mail....

Kez

Yes, I got that same letter. see my time line below.
As you can see in the time line, yesterday I received my wifes NOA1 and today received her appointment for her biometrics.

Soon my friend.