FormsCentral is releasing weekly updates (usually on Tuesdays). Are you sure you are updating when it ask you too? You can't sign in into the FormCentral desktop application unless you actually update the application.
So if you open the application on Monday and you have not opened it in more than a week then it will ask you to update. We will deploy a new update on Tuesday so if you open FormsCentral again on Wednesday it will ask you to update again.
If you use the application daily you should only be asked to update once a week.