The survey will get locked if it is been updated simultaneously by another user. When you open the project settings survey on the projects page, it will appear in its read-only mode.
The survey should unlock itself after 30 seconds, if the user closes the page.
To unlock the project when the survey is not been updated by another user, he can do so by going to the page that lists that project and click on "unlock project" link, it should be located on the right hand side of that column. This would unlock the survey for him, as shown in the Screenshot below.
You can see who has locked the settings from the project list page of the particular application. The user who has locked the settings can also trigger an unlock manually from that page, as shown in the screenshot below.