Forum ERROR: Fatal error: require_once() [function.require]: Failed opening required ..
 

I have been receiving the following errors randomly when posting a new post in a thread. Does anyone know how I can resolve this problem? Thanks in advance.

Warning: require_once(./includes/vba_cmps_plugin_newpost.php) [function.require-once]: failed to open stream: No such file or directory in [path]/includes/functions_newpost.php(643) : eval()'d code on line 1

Fatal error: require_once() [function.require]: Failed opening required './includes/vba_cmps_plugin_newpost.php' (include_path='.:/usr/lib/php:/usr/local/lib/php') in /home/magicdec/public_html/forum/includes/functions_newpost.php(643) : eval()'d code on line 1