PasswordStrength Contrlo in Ajax

Question

Hi

  Respected Sir,

   This is Murali Krishna I am developing one application usinga ajax PasswordStrength Control but i can't drag it into form and it shows an error  That is Element 'PasswordStrength' is not a known element. This can occur if there is a compilation error in the Web site, or the web.config file is missing.

Please tell me how can get it.