Sharepoint “An unexpected error has occurred”

By design in SharePoint if an error occurs the user is shown a generic error message “An unexpected error has occurred”. The detailed error messages are turned off for security reasons.

Here's how to get the full error messages

1. Go to the SP site you want to enable it for.
   For example C:\Inetpub\wwwroot\wss\VirtualDirectories\mySPsite.com80
   
2. Open the web.config for editing.
   
3. Find out the following entry
   safemode maxcontrols="200" callstack="false" directfiledependencies="10" totalfiledependencies="50" allowpageleveltrace="false"
   
   And make following changes to it
   
   safemode maxcontrols="200" callstack="true" directfiledependencies="10" totalfiledependencies="50" allowpageleveltrace="true"
   
   And
   customerrors mode="On"
   
   To
   customerrors mode="Off"
   
   
4. Save and close web.config.