FREE VERSION ERROR: Changes Don`t Save

Hi,

Your changes were not saved due to an error (or you made none!).

I have run into an issue with the free version of this amazing plugin which I have been using for years. The one moment it worked fine and the next it just stopped saving new entries and changes. Also does not disable or delete fields. Does not save any action, even when clicking the save button. Please help urgently, tnx!