I have previously had problems similar to your which did relate to RAM. Download and run [MEMTEST] to establish if this is the cause. It takes a while so you will have to be patient. In my case I did have a faulty stick of RAM which was replaced under Warranty and the error ceased.
Did the problem start when you installed the recent stick and have you tried removing it to see if that is your problem lies? Is it firmly seated? These are the obvious things to try first.