If I want to save any changes in a table, previously saved in SQL Server Management Studio (no data in table present) I get an error message:
Saving c
Go into Tools -> Options -> Designers-> Uncheck "Prevent saving changes that require table re-creation". Voila.
That happens because sometimes it is necessary to drop and recreate a table in order to change something. This can take a while, since all data must be copied to a temp table and then re-inserted in the new table. Since SQL Server by default doesn't trust you, you need to say "OK, I know what I'm doing, now let me do my work."