First message, in toolbar:

An error occured, please run Package-Manager from the right-click menu or an apt-get in terminal to see what's wrong. The error message was: 'Unknown error: '<type 'exceptions.SystemError'>'(E:The package mfc4800lpr needs to be reinstalled, but I can't find the archive for it.)'. This usually means that your installed packages needs to be reinstalled.

And answer from terminal when using sudo apt-get remove mfc4800lpr :

Reading package lists... Done
Building dependency tree
Reading state information... Done
E: The package mfc4800lpr needs to be reinstalled, but I can't find the archive for it.