Today I encountered an error when I installing software from ubuntu-software-center.It stop work and said “waiting for another software in process to quit” when I clicked to install a software.Before this,I was installing a software and my system down.This break could be the reason for this error.
I have fixed out just by running this command:

sudo dpkg –configure -a

This should be a bug for ubuntu-software-center and hope this bug be fixed in next version!