IIS get full error message for failed requests

Solution 1:

You will find the errors in the eventlog, but having them in the browser is indeed more convenient (especially during development). To do that: turn on debugging in your web.config. Also, switch custom errors off or set them to "Remote only".

<configuration>
    <system.web>
        <customErrors mode="Off" />
        <compilation debug="true" />
    </system.web>
</configuration>