It means you are already installing something or upgrading in the background.
Try 'sudo pkill apt' in a terminal without the quotes of course. ** Changed in: software-center (Ubuntu) Status: New => Invalid -- can not download software from ubuntu software center. waiting for apt-get to exit https://bugs.launchpad.net/bugs/662581 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs