It's comforting to know that someone else is experiencing the same problem as me. Incidentally, my page only uses one field for users to search a date. I was hoping that Form Builder would let me change the form so that users can type the date as dd/mm/yyyy.
It appears that this IS the functionality of Form Builder, however after several communications with Eric, it appears that the problem may not be a straightforward one. Eric has managed to replicate the issue on a WebAssist local server using the files that I sent him, however when he created it his end without using my files he did not get the error. As a result he has passed this on to a WebAssist engineer for further analysis as of yesterday and I am currently awaiting a response.
My thoughts are, this might be an error which is fixed in an extension update but whatever happens I'll update this thread when I hear more :-)