Failed opening required 'webmail_plus.filter_functions.inc' (include_path='.:/usr/lib/php:/usr/local/lib/php') in webmail_plus.m

Fatal error: require_once() [function.require]: Failed opening required 'webmail_plus.filter_functions.inc' (include_path='.:/usr/lib/php:/usr/local/lib/php') in /home/example/public_html/sites/all/modules/webmail_plus/webmail_plus.module on line 1253

I removed require_once "webmail_plus.filter_functions.inc";
and changed $user_filters = _webmail_plus_get_filters();
to $user_filters = false;

Fatal error: require_once() [function.require]: Failed opening required 'webmail_plus.charset_functions.inc' (include_path='.:/usr/lib/php:/usr/local/lib/php') in /home/example/public_html/sites/all/modules/webmail_plus/webmail_plus.functions.inc on line 66
I created an empty file.

Fatal error: Call to undefined function decodeHeader() in /home/example/public_html/sites/all/modules/webmail_plus/webmail_plus.functions.inc on line 73
I added function decodeHeader($text){return $text;}