Errors occurred after changing theme

We changed the theme of our website recently and now we receive the following error at the top of one of our forms. My developer has left me and I have no idea how to fix the problem. Here is the error.

* warning: highlight_file(Array) [function.highlight-file]: failed to open stream: No such file or directory in /var/www/highlightgolf.com/htdocs/includes/theme.inc on line 170.
* warning: highlight_file() [function.highlight-file]: Failed opening 'Array' for highlighting in /var/www/highlightgolf.com/htdocs/includes/theme.inc on line 170.

I have narrowed the problem down to the function that is causing the problem. The file with the function is attached. If I comment out the upload form field, the error disappears. If I leave the upload form field the error appears and the field does not show up.