How to set Default Page in IIS Server in ASP.Net

I hosted a website with url 

http://www.savidhareminerals.in/Authentication/Login.aspx

When login with http://www.savidhareminerals.in url it has to move to dashboard because i set login page as start up page in web.config but it's giving an exception.

When i login through below url it perfectly works.

http://www.savidhareminerals.in/Authentication/Login.aspx 

demo :  https://ibb.co/g4q5ak