[ProStructures CE (local build from latest code from RE repo as of 12/27/2021), C#] Error attaching ECData to Element.

Hi, I am trying to attach data of an ECClass to an element and keep getting this exception:

Bentley.Exceptions.EnvironmentalException : CreateInstanceOnElement failed with error code: 6

This is NOT my first ECData class or schema. I have created 3 others (about 2 years ago) that work fine. 1 is ECXAttrubutes and it attached to the DgnFile, the other 2 are ECXData and are attached to Elements.

This new Schema  imports successfully, but throws the exception when I try to attach to an element as follows:

DgnECInstanceEnabler instanceEnabler = DgnECManager.Manager.ObtainInstanceEnabler(ActiveDgnFile, baseDataClass);
if (instanceEnabler.SupportsCreateInstanceOnElement)
StandaloneECDInstance instance = instanceEnabler.SharedWipInstance;
IDgnECInstance dgnInstance = instanceEnabler.CreateInstanceOnElement(callout, instance, false); // <<-- exception is thrown HERE
SetProperties(dgnInstance, bData);

callout is a TextNodeElement

instance is the correct ECClass from my schema

I modeled this new Class and the import and attachment process after one of my existing ECXData classes and for whatever reason it is not working?

I have tried stripping my Class down to barebones and still I get this exception.

I feel like I'm missing something small but, unfortunately, "failed with error code: 6" is not very helpful?