ERROR HANDLING AND LOGGING
Umbraco has a reputation for generous error logging; some even say that Umbraco's verbose error and event logging is too much. When you have an issue with your Umbraco site, the error log is an invaluable tool in helping you discover the cause. By default, Umbraco creates a log entry for nearly all events, errors, and custom logging routines, but you can adjust what Umbraco logs by updating the log configuration.
As Umbraco is really an ASP.NET application at heart, errors that are generated within the ASP .NET runtime, and not handled by an error handling routine, will generate an entry (or two) in the Windows event log. This log can be hugely beneficial to developers creating custom code for Umbraco and also for helping to identify issues in third-party packages and code used as part of your Umbraco site.
The Umbraco Error Log
The Umbraco error log is the table umbracoLog in your Umbraco site's database. Because the log is located in the database it offers another good reason to have the Microsoft SQL Server Management Studio installed because viewing the table is much easier. A number of Umbraco packages are also available that allow you to view and manage the contents of the umbracoLog table. You can find these packages in the Projects section of the Umbraco Community site (http://our.umbraco.org/projects/).
As mentioned earlier, the Umbraco error log creates entries for nearly all errors and events in Umbraco. You can change what Umbraco logs by ...