Found it after much digging.
The StoredProc was returning a LARGE TEXT field (ie. Memo or Blob) which CR4E can process from a Table-source, but not from a StoredProc-source.
We rebuilt the StoredProc to return STRING(8000) formatted values - rather that the unsupported field-type.
That being said, the CR4E tools & connections need to be updated to support those "standard" field-types from TABLES, VIEWS or StoredProcs.