Page Type Fields

I'm have a field for one of my page types called "CategoryGUID", I'm trying to retrieve this value. I can get the node, but when I try and retrieve this fields value I get null each time.

I've tried node["CategoryGUID"] and node.GetValue("CategoryGUID")

Neither will return the value. But if I click on the node and go to the form tab. I can see the field has data in the text box field.