Asp.net – error when trying to access working webpage

I have created an asp.net webpage and have uploaded it onto a webserver. However when I try to view the page remotely, I get errors about the customerror tag in the web.config file. The page works locally with no errors or warnings. Also if I upload the page as a .html file, I can view it fine remotely.
I have seen a lot of other people with this error, but the 'solutions' just say to change the customErrors tag to 'Off', which I have done and does not work, do you know is there an issue with the webserver or what could be the problem here?

Here is the error page:

Server Error in '/' Application.
Runtime Error
Description: An application error occurred on the server. The current custom error >settings for this 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 tag within a "web.config" configuration file >located in the root directory of the current web application. This tag >should then have its "mode" attribute set to "Off".

<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 >configuration tag to point to a custom error page URL.

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

And here is my web.config file:

<?xml version="1.0"?>
<configuration>

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

  <system.web>
    <compilation debug="true"/>
    <authentication mode="None"/>
  </system.web>
</configuration>