Symptoms:

Your ASP.net based site gave you an error message like this:

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 <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>

You have, however, already changed the customErrors mode parameter in the WEB.CONFIG, and you're still getting this message instead of the detailed error.

Resolution:

In general, this occurs because .Net encountered an error in processing your web.config file that occured BEFORE it got to the customErrors parameter, so it handled the error using it's default functionality, which is not displaying the error detail for security purposes. 

This can be for any number of reasons, one common one being you have a database connection string in your web.config file, and either have some problem with the enclosing quotation marks or perhaps your password has special characters in it that are causing problems with the web.config parsing. 

If you're not able to identify the problem, submit a support request describing what you're experiencing and this article - the support team can check the application event log on the server which generally should post any errors (including the specific line and character of the web.config file) where the parsing of the web.config file encountered the problem.