Site Default page does not work after the asp.net upgradation (2.0 to 4.0)

Hi All,
we are upgrading the asp.net 2.0 web application to asp.net 4.0. 
we have the many sub folders with default page (default.aspx)
and we are using the link like,
<domainname>.com/
<domainname>.com/folder1/
<domainname>.com/folder2/
<domainname>.com/folder3/
<domainname>.com/folder4/
it is working fine in asp.net 2.0
after the upgradation process,  we didnt get above the  URLs. i have checked site default page settings (in IIS "Document" default page settings), and default.aspx page is shows under settings.
 
the site url  "<domainname>.com/" also does not working. if we call "<domainname>.com/default.aspx"  then worlking.
 How can i fix that error?
...