Well, for one I don't know why you would do that, dual channel is a lot faster. You might consider buying 1 more stick of the same RAM, or just removing one. 6gb RAM doesn't really do anything over 4gb either if you're gaming.
But anyway, I don't think that would cause blue screens. If they are caused by the RAM, then it might have to do with improper timings. You should consider entering your BIOS and trying the XMP profile settings - that is, if it's DDR3 - otherwise do it manually. Could be 1 faulty stick of RAM too. You might want to run Memtest86+, you have to put it on a floppy or CD/DVD and then boot up with it. If there's any RAM issues it should tell you.