Enable Debugging in SharePoint

In WSS 3.0/MOSS 2007 to enable debug information we have to modify only the web.config related to your web application.

Instead, in SharePoint 2010, we have to modify two different web.config files:

1.the one that you can find in the root directory of the web application in which you want to debug you customizations (the file at the path: [drive]:\inetpub\wwwroot\wss\virtualdirectories\[port])

  2.the one that you can find into the "LAYOUTS" directory under the SharePoint root (the file at the path: [drive]:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\LAYOUTS)

What remains unchanged from the previous version of SharePoint are the number of attribute to change in the web.config file:

•The "debug" attribute of the "compilation" element has to be set to "true"
•The "callstack" attribute of the "safemode" element has to be set to "true"
•The "mode" attribute of the "customerrors" element has to be set to "off"

This is from this site: http://www.dev4side.com/community/blog/2010/8/16/how-to-enable-debug-information-over-exceptions-on-sharepoint-2010.aspx