Adding a formula to the selected column will delete all relationships it participates in as a foreign key. (Visual Database Tools)
SQL Server 2005
The column to which you are adding a formula contributes to one or more foreign keys. The modification will delete the attendant foreign-key relationships. Choose Yes to proceed with the modification and delete the relationships. Choose No to cancel the modification.
Concepts
Error Messages in Visual Database ToolsOther Resources
Computed ColumnsCreating Indexes on Computed Columns