Spent some time trying to figure out what was wrong with this due to vague emails from staff saying "teh surveh iz broke, plz fix kthx".
"Everything is urgent! Please fix immediately! I'm so important!"
After a bit of trial and error, the horribly worded error is due to a character limit imposed on the input field.
If your field is limited to 100 characters and the user inputs 101 or more characters, they'll get this vague error.
Just be sure to let them know of the limit in the description or something.
Good old trial and error.