As Technical hand we know that the first step for troubleshooting will be the Error page or error code. We won't get actual error if the custom errors mode is in ON state. Yes we can turn it off through this steps,
1. Open web.config file
2. Find out the following line <customErrors defaultRedirect="errorpage.htm" mode="RemoteOnly">
3. Replace it with <customErrors defaultRedirect="errorpage.htm" mode="Off">