Cannot ALTER TABLE in MS SQL
There is a new option added in SQL Server 2008/2012 for modifying tables while using the Table Designed in Management Studio which will prevent saving any changes to a table that needs a drop/re-create of the table.
The error you see
User canceled out of save dialog
(MS Visual Database Tools)
Tools ->Options-> Designers -> Table and Database Designers -> uncheck the option “Prevent saving changes that require table re-creation”