By default saving changes on a table is is blocked. When we want to change or alter any Table Then it shows following message
Saving change 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 cant be re-created or enabled the option Prevent Saving changes that require the table to be re-created.
We can fix it following way
Tools Menu >
And un check the option “Prevent saving changes that require a table re-creation”