Changing a Parameter in a data function. Cannot associate Output variable with a new Document Property

I am running a data function which has an ouput parameter that is a document property I created initially.

I have created a new document property and I want to use it for the parameter instead of the original one.

When I am in the Edit Parameters screen for the Data Function, it lets me pick the new Document Property name but I cannot save the new setting (the button "OK" stays shaded, so I can never get back to the screen where the button "Save" is).

How can I fix this. Do I have to recreate the whole data function from scratch?.

(1) Answer