There are times when you get an error stating
"Saving changes is not permitted. The changes you have made require the following tables 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."
You can easily resolve this issue by following the steps mentioned
1. Launch SQL Management Studio and connect to your SQL Server instance.
2. Navigate to Tools -> Options.
3. In the Options dialog , select Designers in the left sidebar and then uncheck the option "Prevent saving changes that require table re-creation" and click ok.
This should solve the above issue.