I'm having a real problem with this one too!
It seems to have appeared out of nowhere with a form I've been happily using for 18 months! Surely it must be the recent update? I've just noticed the recent update note says:
(12 May 2012) - Better detection of checkbox config errors.
Thing is . . . . I've checked my coding via the FastSecureContact Form website instructions. see link
and I can't see any error!!!
The code I used in 2 of the extra fields (when I originally built the forms 18 months ago) are as follows:
The form which these parameters are used in is here:
Any ideas anyone?