I have looked all over the help/support/answers site for any documentation concerning the creation of custom errors and how to use the Error Catch/start/end functionality... Where is it hiding? does it exist? 
Hi Michelle,
Is this what you are looking for, in which case as per the response to it, Try/Catch functionality may be available in the Forms 11 release.
Regards,
Mike
Error catch/start/end event are new features added in Forms 10.2, you can refer to the documentation here.
I found this - but there are 14 lines of information describing the functionality - but no examples... sorry but I'm struggling to understand how to make them work. I have to create a custom error on the END first that throws to a CATCH on the sub-process - where's the start? is it needed?
I have tried it - this is what happens:
User submits a form
Bad supervisor email is entered
System notes that it was caught - and it skips the step that the error happens on and moves on along through the process without completing the step that the error happened in.
Supervisor Approval Sub process
The error event is not supposed to throw error when system error occur. You use error end event to throw self-defined error, then use error catch event to catch that error and do some action. An sample would be like following:
In the sub process, check the field variable to decide whether bad field values has been submitted in previous user task, if do, then sub-process will go to error end event and throw customize error.
In the main process, use error catch event to catch the customize error and perform some action.
An error start event is to catch the error if the error is not caught by error catch event.