I don't normally post on these kind of things, however I have read though all the posts containing these issues and followed instructions as to how to work out what the problem is.
It works sometimes - In fact just over half of the time I would say. But when it doesnt it just gets stuck with the error message again and again - obviously this is not suitable for my customers.
However the debugging post you made was of no use to me, I have turned on debugging and I have no error messages coming up on any of the skins I am using - I have 4-5 websites atleast using the same contact form.
PHP register_globals is definatly off, and I tried using the - start session bug fix you suggested just in case that was the problem and it made no difference.
I would appreciate a reply as I love this contact form and the it is one of the least bulky contact forms with a captcha I have used, it would be a shame to have to change.