Multiple asp.net form authentication in a single domain

Hi All,
We are upgrading the asp.net 2.0 web application to asp.net 4.0. 
 The application contain three main modules (sub application) like End User, Franchise and Admin with separate web.config, asp.net form Authentication, login page and running with single domain.
 the URL like,
mydomain.com/login.aspx
mydomain.com/franchise/login.aspx
mydomain.com/admin/login.aspx
 In asp.net 2.0, working fine with 3 sub applications with separate form authentication under a single domain name and also we can working with all threes in same time.
 After the up gradation process (ASP.NET 2.0 to 4.0),
We didn't run all three applications in same times and also form authentication crossed.
 How can I fix that error?
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