Symptoms

Create Reference event fails when reference is not first declared in parent workflow.
 

Diagnoses

The issue seems to do with WHEN References are declared. It appears that one cannot use any named reference in a sub-workflow that has not already been declared in the primary workflow.

So for example, this workflow would error on the "Create User Reference"

Workflow 1
- Call workflow 2

Workflow 2
- Create User Reference "foobar" for user "Bob Smith" <- Error Here
 

Resolution

The following solution was successful:

Workflow 1
- Create User Reference "foobar" for any user (existent or nonexistent in the system I used "myxzptlk" and it worked fine)
- Call workflow 2

Workflow 2
- Create User Reference "foobar" for user "Bob Smith"

So what it appears is that all reference must be explicitly declared (not loaded with a valid object, but declared) in the primary workflow to be used in any subsequent sub-workflow(s).