error in TagPrefix while registering Ajax on Login.aspx form

Question

Dear Friends,
I am using the Ajax controls in my web project.
at the time of using the Tools "TextBoxWaterMarkExtender" the registry get registered like below:

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %>

i m having a doubt in TagPrefix which should been like TagPrefix="cc1"....and which i am getting is diferent...for that reason i am unable to use the Ajax Controls.
Pleas let me know what is the Error?

Thanks & Regards,
Aamir