The answer is on the MSDN site:
The Save (Not Permitted) dialog box warns you that saving changes is
not permitted because the changes you have made require the listed
tables to be dropped and re-created.The following actions might require a table to be re-created:
- Adding a new column to the middle of the table
- Dropping a column
- Changing column nullability
- Changing the order of the columns
- Changing the data type of a column
EDIT 1:
Additional useful informations from here:
To change the Prevent saving changes that require the table
re-creation option, follow these steps:
- Open SQL Server Management Studio (SSMS).
- On the Tools menu, click Options.
- In the navigation pane of the Options window, click Designers.
- Select or clear the Prevent saving changes that require the table re-creation check box, and then click OK.
Note If you disable this option, you are not warned when you save the table that the changes that you made have changed the metadata
structure of the table. In this case, data loss may occur when you
save the table.Risk of turning off the “Prevent saving changes that require table re-creation” option
Although turning off this option can help you avoid re-creating a
table, it can also lead to changes being lost. For example, suppose
that you enable the Change Tracking feature in SQL Server 2008 to
track changes to the table. When you perform an operation that causes
the table to be re-created, you receive the error message that is
mentioned in the “Symptoms” section. However, if you turn off this
option, the existing change tracking information is deleted when the
table is re-created. Therefore, we recommend that you do not work
around this problem by turning off the option.
