Configuration file Web.config is not recognised

Question

I develop a application with my friend implemented in Asp.Net and I have strange problem.
I downloaded the newest source code from our ftp server (We haven't install source control tool yet) and when I tried compile and run application, IIS throw exception. I checked directory and there is a web.config file.
I don't get it what's wrong:(. Thanks for a help:).
this what the IIS response:

Runtime Error
Description: An application error occurred on the server. The current custom error 
settings forthis application prevent the details of the application error from being 
viewed remotely (for security reasons). It could, however, be viewed by browsers 
running on the local server machine.

Details: To enable the details of this specific error message to be viewable on 
      remote machines, please create a <customErrors> tag within a "web.config" 
      configuration file located in the root directory of the current web 
       application. This <customErrors> tag should then have its "mode" 
       attribute set to "Off".


<!-- Web.Config Configuration File -->

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


Notes: The current error page you are seeing can be replaced by a custom error page 
by modifying the "defaultRedirect" attribute of the application's <customErrors> 
configuration  tag to point to a custom error page URL.


<!-- Web.Config Configuration File -->

<configuration>
    <system.web>
        <customErrors mode="RemoteOnly" defaultRedirect="mycustompage.htm"/>
    </system.web>
</configuration>

Answer 1

Oh my gosh!!! I found issue. I haven't checked in windows explorer option 'show all known file extentions' and I saved web.config with txt extention and I haven't seen that ridiculous error. Thanks for a help!!!

Answer 2

You need to add the section to your Web.config so you can see the actual exception.

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