Troubleshooting ASP.net Application with CustomErrors

There are many ways to troubleshoot IIS application errors. Here I will discuss a simple yet effective way to troubleshoot your IIS applications.

In the Web.config, under System.web node, there's one section called customErrors. By default this is commented out and the mode set to

<system.web>
<customerrors mode="RemoteOnly">
<system.web>

With this setting in place, if you run into some error, chances are you will only see a generic runtime error that reads:

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.

In order to see what's going on, you will need to modify the Web.config file so the customErrors tag read:

<system.web>
<customerrors mode="Off">
<system.web>

Note that this should only be done on development workstations as the detailed error message could expose information you don't want users to see like identity impersonation information... As for production, try to run the application on the server to see the error.

Now that you can see what's actually causing the error, it should be easy to narrow the problem to a particular line number and take corrective action.