I found a bug on filesystem module.
If one tries to send file as an email while the file is being edited, following error occurs:
Warning: main(email.class.inc) [function.main]: failed to open stream: No such file or directory in /home/xxx/xxx/modules/filesystem/properties.inc on line 30
Fatal error: main() [function.require]: Failed opening required 'email.class.inc' (include_path='.:/usr/local/lib/php') in /home/xxx/xxx/modules/filesystem/properties.inc on line 30
The reason: On line 30 of properties.inc of Filesystem module $email_module['class_path'] gets called but $email_module is not defined yet.
So, just add
$email_module = isset($GO_MODULES->modules['email']) ? $GO_MODULES->modules['email'] : false;
on line 26 and upload file.