When I try to de-activate any plugin it gives error “Warning: call_user_func_array() [function.call-user-func-array]”

The Youtuber plugin has a little error: it has a function to remove it’s own options, called wp_youtuber_uninstall. However, it hooks into the deactivate_plugin option with the function youtuber_uninstall, which does not exist. This has been reported in the WP support forums.

You can remove the line that says add_action('deactivate_plugin', 'youtuber_uninstall' ); to get rid of this error. In fact, be happy that it doesn’t work, because the wp_youtuber_uninstall function should check which plugin is being uninstalled right now, and only clean up when it is remove itself. Right now, it would remove its own options every time any plugin is uninstalled.