An unexpected error has occurred at Save

Hello, first of all I would like to congratulate you for such a simple and efficient plugin.
But today it gave me an error, which prevents me from using it or testing it.
Yesterday I was doing tests with small forms, without any problem, I could edit, save and the tests were sent correctly. Today I have finally decided to upload the PDF, but I find that when I press the save button it does not save it. I get an error message, “An unexpected error has occurred. Please try again.”