Bug in settings (if upload directory is unwritable we won't be able to change settings)

If we set upload directory unwritable we won't be able to set new configuration, change upload directory. We will always see 2 errors:

* The directory {current_directory} is not writable
* The settings have not been saved because of the errors.

and the new settings won't be saved.

In my opinion it is caused by not cleared error message (we've got error message in a setting view, and that's why everything fails.