Did you create the same aggregates in the second part?
Dont forget: comboboxes has to have 2 main parts:
1. The data source. Where you get the info to list. In general are aggregates.
2. The data destiny. Where you will store the selected info. In general is a field inside a form, most of times Identifiers.
If your getting problem with the list (no show) , probably the problem is in the first step. Aggregates. OR... properties from the combo as well.
Try to review all of this, maybe you can find the problem. Good luck.
Hope to help you. Rgrds, Rodnei.