Uninstall not working, makes plugin update fail as well ...

[Hansaplast]

When trying to update version 4.0 to 4.1, Wordpress fails with the message that it could not remove the plugin.

Manual uninstall of the plugin fails as well:

WP Error:
Plugin could not be deleted due to an error: Could not fully remove the plugin(s) wordpress-backup-to-dropbox/wp-backup-to-dropbox.php.

Setup:
Wordpress 4.1 MU
PHP 5.4.30
Apache 2.2.27
User/Group: nobody

Please advise on how to do this manually (removing the directory will work?) and/or address this in future releases?

Note: installing premium add-ons for this plugin failed as well, and "support" was not able to resolve this issue either.