Captca Error: "You filled out the form incorrectly"

Hi, i just got a message from a customer that my custom contact fields is not working – i am not sure how long it has been broken or what the cause was, but i know two things:

This error message is coming up:
You filled out the form incorrectly.
• You copied the number from the captcha field incorrectly.

and

Warning: array_merge() [function.array-merge]: Argument #2 is not an array in /home/jonesbay/public_html/wp-content/plugins/w3-total-cache/lib/W3/Request.php on line 106

Comes up when W3 Total Cache is active.

Can anyone please help me??

My form is located here

Thanks!!!