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.
When getting this error in SQL Server Management Studio 2008, be aware that when you redesign a table is a way that affects it's structure, the action requires the table to be recreated. By default the Database Management Studio will not allow you to recreate it, therefore no changes allowed.
The solution is simple.
1) Go to Tools -> Options
2) Select the tab Designers and inside of it Tables and designers
3) Uncheck Prevent saving changes that require table re-creation
4) Save
This configuration is very obvious, but the path to it is rather obscure so it is here for future reference.
