I would like you to test the following with the file I provide to you and see if you get the same results. After hours of testing I decided to start a php file from scratch (not saving a .htm to .php) with the customized form only (no copy or css from my original document). That seemed to work excellent.
This led me to do the same for the contact page and copy paste all my content into that. After a couple of hits...well...the rest were consistent errors. Tried different scenarios but throughout I have been thinking that maybe the chat box and the skype tool are causing the problem. When I took the skype option out it still gave me errors. But then, eureka, taking the yahoo tool out made it work like a charm.
So my request is that you try this on your end with the file I sent you (removing those items that is) and see if you get it to work. I really would like to have that chat functionality on that page so if you come to a solution soon please let me know.
In the meantime I will test it on my end (removing items from the original contacts page) and see if it work form me again.