I installed Ubuntu with Mate as the GUI for a friend, the computer is an Asus S301L. It worked fine for a while, but then he said that it was failing to boot. He says he didn't do anything other than updating the system as requested by the update manager.

What happens is that the starting screen - the one with all the [OK] statuses - flashes a few times, then I get a text login prompt and a line saying the crash report daemon has been started.

I can login in text mode, and reading Xorg.0.log I find that error.

If, at this point, I manually do startx, the GUI does start and autologin, but it's all broken - the panel doesn't appear, for instance, and alt+f2 does nothing. I get a desktop with the various icons the user put there (mainly images and pdfs). I can open them, the relevant apps do start, but I can do nothing else.

fsck comes up clean, by the way.

Any ideas how to solve this? I'd really rather not have to nuke from orbit. I Googled, but I can only find old bug reports. I did an apt-get dist-upgrade from console in case there were broken packages; it did its thing, but it solved nothing.

dmesg, Xorg.0.log. There is no xorg.conf.

I gave up using rpm packages and never started on debs basically to avoid your problem. If you have manually compiled stuff or even the wrong combination of packages, or a repaired disk fault, this sort of thing can come about. The more you update, in my experience, the sooner it comes about.

Some situation exists like the wrong lib linking to a whole lot of your vital stuff, or corrupt files due to disk error, or something imponderable. It may be hardware.

If you don't want to reinstall (and I never do), can you do some command to reinstall and overwrite all existing packages? That might sort it.

Moved: This thread is more suitable in <Ubuntu> and has been moved accordingly to help your thread/question get the exposure it deserves.

What version of Ubuntu+MATE? If it is Ubuntu 14.10 it is a development release and isn't something that should be dropped onto new users.
If is 14.04 and older MATE is only available by PPA and again I wouldn't drop that on a new user.
Let us know what version it is so we can at least try to give better responses.