http://social.technet.microsoft.com/Forums/en/w7itpronetworking/thread/7ad3a4a5-0a0f-4e7e-85d0-ca306f873c4e - search for 'HOW TO FIX WINDOWS DELAYED WRITE FAILED VIRUS:'). Whether this solved the problem with system check, or whether there was another problem I'm not sure.
Rebooted, and got another problem. A screenshot looks the same as http://www.bleepingcomputer.com/virus-removal/remove-internet-security-2012.
I tried following the steps in the System Check Uninstall Guide, but in Safe Mode (with Networking) RKill isn't finding anything, and TDSSKiller doesn't run (looking in Task Manager I can see it startup but it closes down within a second). I've tried running DDS to get a log, but the process gets to about three quarters of the way through (based on the number of hash tags running across the screen at the bottom showing progress) and then hangs without a log popping up - it also takes a lot longer than 3 minutes to get to this point. I've run GMER, but the boxes from System to Libraries are greyed out, so I can only scan Service, Registry, Files and C drive and am unsure how thorough the scan is. I've attached ark.txt from GMER.
Any advice on running DDS, running GMER or removing Internet Security or System Check?