Error in Login And Logout

Hellow .,
I have configured the fba on my site and installed the fba pack as per Instruction . but when i enter site name such as http://sharepoint:port/ it gives error . when i append _login/default.aspx. it works great. when i logout it also gives same error . error is bellow

'System.ArgumentException' was thrown.
Parameter name: encodedValue
could not understand what to do . Please Help me .
Did you configure a custom login page for the Web Application? (Central Admin -> Manage Web Applications -> Your Web Application -> Authentication Providers)

If you didn't, it should redirect you to the login page automatically. If you did, there could either be something wrong with your login page or the url entered. Try setting it to use the Default Sign In Page, and see if it starts working again.
Thanks Very much for reply. my problem has been resolved
i don't know why problem was arising during login and logout time as described above. but today morning i tried to see it . just working fine
thanks again once.