From Hostek.com Wiki
If you are seeing custom errors that you did not set, or you are not seeing the full error reporting you wish, there is a setting that controls the debugging output for ASP pages.
There is a simple way to turn this feature On or Off in the IIS control panel of your server.
- 1: Open IIS control panel on your server.
- 2: Select the site you wish to enable or disable debugging for.
- 3: Click the "ASP" icon.
- 4: Find the tab that says "Debugging Properties" and expand it.
- 5: Send Errors To Browsers to "True" if you wish to display the errors, or "False" if you wish to hide them.
- 6: Click "Apply".
You may wish to restart the IIS service to complete the change. This can be done by accessing the command prompt on the server an running the command
iisreset in the console.