It is likely the code is trying to include a file during the loading of the page. Could you post the source code of the page before it is executed by the server? To do this you will need to copy and paste what is in one of the pages by logging in to FTP and viewing it there. We will need to see what code is in the place of the error message before the code is executed, and the best way to do this will be to open up the page in your FTP program and copy and paste the code.
I can't see anything in the code which would cause this. Have you checked with the Web host to see if they are adding anything at server level which may be causing this?
I have just checked your site, there doesn't seem to be an error now, what was wrong in the end?