acunetix security bug "long password denial of service"

hello guys i run my asp application in server and check this security test with acunetix my application has 1 high security bug ("long password denial of service") i try some solution to fix it :

-add asp validator with 15 character limitation
-check password length with java script
-check password length on server side
-put an captcha on my login page

But had no effect and still gives an error "long password denial of service"

Please Help me ! whats wrong!? Do you think that acunetix mad