In SQL Server Management Studio 2008 / R2, the default designer behavior is to disallow changes to tables where the table will be dropped and re-created by SQL Server for you (this is normal, it just happens without your knowledge for the most part). If you’re new to Management Studio 2008, then you might be wondering why the following dialog appears when you amend your table schema, by adding a new column for example.
Basically, this will not allow the table update to take place and you select ‘Cancel’ to kill the dialog.
This is a very easy problem to fix as this warning is shown only because the default setting is checked when you install Management Studio. If you make your way into Tools > Options and select the Designers tree node, you can un-check the ‘Prevent saving changes that require table re-creation’ option under Table Options.