Saving changes is not permitted. The changes that 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.

Normally I don’t like copy/paste solutions but I also can’t stand wading through Microsoft issue explanations. This is how you fix it in quick picture form:

Tools -> Options -> Designers

The worded Solution is from here.

While trying to save changes to a table, it’s because you’ve done this:

• You change the Allow Nulls setting for a column.
• You reorder columns in the table.
• You change the column data type.
• You add a new column.

And there it is folks, simple and done with.