If your site having error 500 Internal Server Error and you need to find out what is the actual line error inside the code, you can ask your web host to set from IIS (version 7.xx) as below :
1. From your server IIS, click your domain.
2. Double-click the ASP icon.
3. Under Debugging Properties ensure that Enable Server-side Debugging and Send Errors To Browser are both set to True .
Don't forget to Apply your changes.
4. Go Back in the main window, and double click Error Pages.
5. Click "500" in the Status Code column and click Edit Feature Settings... in the right side.
6. In the Error Responses section, please select : Detailed Errors.
You are done.
You can now test your site again if the detailed error can be displayed.