With SQL Server 2008, MS introduced an updated Management Studio tool.

One change within this stops users from making many changes to a database once first saved. Changes, such as adding a new field amongst the existing fields, results in the following message:

"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."

The good news, is that in the vast majority of cases, the change that you're trying to perform is entirely harmless. Although the database table may need to be dropped and rebuilt, you'll end up with the data still in the table and working.

Even better news, you can override this behaviour in the MS Management Studio options, by clicking Tools > Options > Designers and unticking (or unchecking, I guess) "Prevent saving changes that require table recreation".