%20/Space Added to a redirected URL

I go to this website http://test.domain.com and it is redirected to this site based on a scripts sitting on IIS7 windows 2008r2 serverhttp://login.domain.com/zk_auth.asp%20?

After the rediection a logon dialog box pops up and when I enter the credentials the page crashes with this address http://login.domain.com/zk_auth.asp%20 and when I remove the %20 at the end and hit enter it works just fine and I able to successfulyl logon.  I am not sure where/when is this SPACE/%20 added.  Nothing is inthe script either.  Same issue on IE8 and Firefox.

Any ideas - Thanks?