When hitting the SP initiated URL, the browser lands on a 404 page of login.fcc.
The login page can be displayed correctly when the browser hits the IDP initiated URL without any parameters.
URL is over 2048 characters long.
IIS 7.5
URL is longer than IIS' maxQueryString.
The browser receives the IIS return code 404.15. This means "The Request Filtering module rejected a request with a too long query string" (1)(2)(3).
To fix this, increase the value for maxQueryString. It has a default value of 2048, and the browser request query string is 2,248 bytes.
To do this, edit IIS' web.config:
<system.webServer>
<security>
<requestFiltering>
<requestLimits maxQueryString="4096"/>
</requestFiltering>
</security>
</system.webServer>