Using Data dictionary structures for page attributes

Hi, very new to BSPs but hopefully this is not a totally stupid question.

I have a page attribute defined as a type from the data dictionary, BAPISDHEAD.

When I try to transfer values with the navigate->set_parameters the page errors and will not display.

When I use a structure, defined by myself as a local definition, the tranfer of values is okay and the page displays.

Any ideas why the ddic structure does not work.

Thanks