In order to track and configure certain errors click on an error to be able to drill down on the errors transaction snapshots.

Errors are listed in the Exceptions summary on the Application Dashboard page.
The number of errors does not correlate to total number of exceptions

To configure the error monitoring:

Under Configure -> Instrumentation->Error Detection-> Java Error Detection

Here you can specify where to detect errors, set up custom loggers, ignore certain exceptions and messages, specify certain HTTP return codes to be errors, and detect errors based on redirect pages.
The configuration changes you make will be viewable on all Tiers.

You can start your error troubleshooting by accessing the list of errors snapshots from the Application Dashboard. You can also go to Troubleshoot->Errors. From here you can click on the Exceptions Tab to see a list of the types of errors that have occurred in your application over the selected time range. You can also see where and how often the errors occurred.