Just thought I'd add this note as I have spent half a day trying to understand why my WIFI connection kept on failing at the authentification stage following a complete upgrade using UP4 and the update manager.
After a complete backup of my Lenovo G570 laptop using [url]Redobackup[/url] - great tool with the live CD for saving all partitions to LAN or connected HD - I had tested it using a 201204LMDE that I'd burnt to a DVD. As everything seemed to work well (including sound & wireless connection) I decided to go for the complete upgrade using the Mint tool with UP4 and the update manager rather than via the command line, as everything boded well. The upgrade took about three hours and there were warnings about gconf2 and other problems that I didn't pay attention to. I accepted all the proposed reconfigurations and then was confronted with the same problem I had when doing an earlier upgrade with my desktop machine - namely it would only reboot to a terminal as the xorg drivers hadn't been installed.
Following an instruction by dritzonimous http://forums.linuxmint.com/viewtopic.php?f=198&t=99281#p565220, I forced installation of the remaining packages that had been blocked for some reason and startx succeded in bringing me back to my favourite Xfce WM. However, I had one remaining big problem and that was an annoying refusal to complete authentification with the encryption key of my router so I had no wireless connection. Curiously it worked the first time when the X-window started as it connected automatically in parallel with my wired connection that I'd been using in case the wireless failed. And yet, on rebooting the network manager went on whirling incessantly as it repeatedly asked for my encryption key. Obviously it was not a problem with the Ralink RT3090 interface as the rt2800pci driver had been correctly loaded and was recognised by lsmod. So looking at the message log I saw that the "Auto My connection" configuration in the network manager window was marked as "invalid" since it was sending "no secrets" during the authentification procedure. So I decided to delete the configuration and restart the wireless connection. It obviously asked me to choose the router and then insert the encryption key again, and then lo & behold it connected with no problem.
agrandir using LMDE with Xfce on a Lenove G570
So I kicked myself for not thinking of this sooner! Half a day wasted hunting through forum messages to no avail. Just thought that it might help if anyone is confronted with the same problem.