HTTP List not copying across Project Areas.

I want to move a work item from one project area to another. The 2 project areas have the same work item types and attributes. When I move a work item across all the other fields move across except for one which is of type string list name = AttributeName. I get the the following message on the top of the page "Type of attribute not supported: AttributeName"

Please advise as we need all the attribute details to move across.

Thank-you,

Kind Regards,

Michael Alberda