Debugging using CallStack Attribute

Windows SharePoint Services overrides the CallStack attribute. This attribute is located in the Web.config file. The CallStack attribute controls whether a call stack and an exception message are displayed when a system-level exception occurs while ASP.NET processes a request to send a page to all local and remote clients. By default, Windows SharePoint Services disables the CallStack attribute and displays a limited set of exceptions to prevent information disclosure. To receive a call stack and an exception message when an exception occurs, enable the CallStack attribute.

To enable the CallStack attribute
In Windows Explorer, browse to the following folder:
local_drive:\InetPub\WWWRoot\bin\

Double-click the Web.config file.
In the Web.config file, search for the <SharePoint> element.
In the <SharePoint> element, locate the
<SafeMode MaxControls="50" CallStack="false"/> tag
and change it to
<SafeMode MaxControls="50" CallStack="true"/>.
Save and close the file.
When exceptions occur, you now receive ASP.NET exception messages with stack trace information.

Note The CallStack attribute enables this functionality for all local and remote clients.

For more information check the source.