How can i add the custom drop down only menu in workspace?

Summary:

I created a custom drop-down only menu in Custom Object from .Net, and I want to add it to my incidents workspace. But I am not able to see it from the Insert field sections.

Content (required):

Hi Guys,

I try to add a drop-down only menu custom object into my incidents workspace. But I can't find it in my insert field section in workspace designer. I am sure I deployed it. In the objects designer ribbon. I only have the Summary button able to click. The rest of other buttons are all disable( Fields, indices, Relationships, and extra options).