combofix "out of memory"?

My laptop has been infected with virtumonde and variants (symptoms...unwanted pop-up ads despite pop-up blocker).
I have been going thru the step-by-step guide in this forum and have gotten through to the combofix part, but combo fix will not run, it comes up saying that it is preparing to run, then gives me the message "Out of memory" and then wont do anything else.
I dont know what to do about this. I have plenty of memory, I have rebooted and still the same.
Should I just skip this step and go on to the MGTools part?
I am not 100% sure, but I think that my problem has been fixed by the steps before the combofix, my machine seems to be running normally again, but I wanted to follow through with all the steps just to be sure.
Thank you for your time.

 

Update: Tried running combofix in safe-mode, at first got the same message, plus and application error, tried again and there were several error messages, but all of a sudden combofix was doing a scan. Not sure what was up with that, but I now have a scan done with a log, now I am on to the MGTools step.
Thanks