HTTP Error 404.0 - Not Found

I have my website online but it's throwing me this error:

HTTP Error 404.0 - Not Found
I made it so you need to login to access the pages, but instead of redirecting me to the right pages, it's throwing this error.

/Account/Login?ReturnUrl=%2f

Instead of Account/Login? it should be Login.aspx?ReturnUrl

How do I change where it's being redirected?
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