We cannot see your screen, however, this error usually occurs when something is missing or not matching. If you are using the desktop version you can flip to forms mode and look for any form that has an error sign next to it, then whichever box is the problem will be highlighted in red.
If you are using the online version, when you get this error, a form should pop up telling you what needs corrected. If it does not, you will need to go back and review your entries and look for something flagged in red.