Unable to cast object of type 'Dynamics.AX.Application.FormStringControl' to type 'Dynamics.AX.Application.FormReferenceControl'

Hello!

I hope you can enlighten me on this.

I am trying to call all 'case categories' and 'category types'. Basically what you see here:

I'm trying to get something similar to the 'Case category' field to appear. But when trying it I get the following error:

Unable to cast object of type 'Dynamics.AX.Application.FormStringControl' to type 'Dynamics.AX.Application.FormReferenceControl'.

I understand that the error occurs when trying to convert the 'String' to the data type that belongs to 'Case category'. But I have created my field with the same properties as the original, and in the 'Category types' I have no problem calling it. I want to know if anyone knows how I could solve this.