When troubleshooting some issues, we need the actual error message instead of the custom error message. Below are the steps to get actual error message in web pages in our SharePoint application:
1. Go to “C:\inetpub\wwwroot\wss\virtualdirectories\<<your web application port>>" and make a backup copy of the web.config file.
2. Open the original web.config file with Notepad and set the following as shown below then save and close the file: CallStack="true", debug="true", customErrors mode="Off"
3. Go to “C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\LAYOUTS” and make a backup copy of the web.config file.
4. Open the original web.config file with Notepad and set the following then save and close the file: customErrors mode="Off",
5. Open our SharePoint application n a browser and repeat the steps that are causing the issue.
6. Take a screenshot of the error and send it to firstname.lastname@example.org
7. Undo the changes by replacing the two modified web.config files (in both places) with the backups.