I have also experienced this error with the plugin running on one of my clients sites. The error is caused by the JS for this plugin being loaded on every single page in the administration panels. This plugin's JS is trying to initialize the syntax highlighting for the two textboxes, but the textboxes are only on the edit/add post screens, and so on the other screens it gives this error.
Serkan, you should stop hooking the enqueue functions from the actions that you have them hooked to, and only call them inside of the function that displays the metaboxes. That way the JS will only be loaded on the administration panels where it is actually needed. I edited the plugin to do this, and the error was fixed. And the plugin still worked on the add/edit post screens.