Carry Custom Error From One BPL to Another BPL

Hello,

I'm trying to carry a custom error from one business process to another.

BPL:LookupClass fails it's lookup and a custom error of "Lookup XYZ" is generated.

The class quits with that error, but upon quitting, the custom error gets wrapped in an Ensemble System error: 

ERROR <Ens>ErrBPTerminated: Terminating BP LookupClass # due to error: Lookup XYZ

This means, when I use the %LastError property to get the error message, it's not got the value I want to use. In this case, "Lookup XYZ". It instead has "Terminating BP LookupClass # due to error: Lookup XYZ"

Is there a way to prevent the Ensemble System error triggering between the two classes so I can use the custom error message?

Thank you for taking the time to read!