Within FusionReactor errors will be tracked when an exception is fired during a transaction or the response code is in the 5xx state.
You can define what errors or status codes will be in the error settings.
For any exceptions fired the stack trace will be captured in the transaction details.
If you have the Ultimate or Developer editions of FusionReactor you will also have access to the event snapshots.
Event Snapshots will capture the full context of any recurring errors (captured from the second occurrence of the error). For each error, you will see the code that broke, a full stack trace and all variables at the time of the error.
Note that for Adobe ColdFusion servers, variables will only be captured on the top frame due to a performance issue within ColdFusion.