Multi Handle Slider Extender Error

                              By Creating the Multi Handle Slider Extender in Ajax in my Design part its showing Error as "Multi Handle Slider Extender could not be set on Property Multi Handle Slider Target" . I am wondering why this Error occurs in my aspx page alone but in Output doesnt show any error. How to solve this issue in my design page ? How it affect my project ?

Guide me plz.....

Thanks

Vignesh