“Saving changes is not permitted. THe changes you have made require the following table to be dropped and re-created. You have either made changes to a table that can’t be re-created or enabled the option Prevent saving changes that require the table to be re-created.“
Finally I knew what is wrong on my Management studio, I have “Prevent saving changes that require the table to be re-creation.” option set.
It is very easy to solve this problem.
1) On SQL Server Management Studio
2) Click on “Tools” then select “Options…“
3) You will then see the screen below popped up.
4) Click on the “Designer” tab
5) Untick the check box which said “Prevent saving changes that require the table to be re-creation.“
6) Click “OK” and try again.
It should allow you to update the table schema.