By default Microsoft SQL Server Management Studio has the option [Prevent saving changes that require the table to be re-created] enabled. This causes an error, when you want to save changes to a table that require the table to be dropped and re-created.
During development you can disable this option: Tools > Options > Designers > Check [Prevent saving changes that require table re-creation]
If your versión is Microsoft SQL Server 2013, you will find the checkbox in Tools > Options >Database tools> Table and Database Designers> Table and diagram options