I've got a new 2011 27" iMac and I ordered 4GB (2 x 2GB) RAM upgrade from OWC. I installed the OWC RAM before I even turned the iMac on for the first time. On the first boot I got a kernal panic error and had to restart. I kept getting the kernal panic errors so I removed the OWC RAM and everything worked fine. I returned the OWC RAM and when I installed the replacement RAM the kernal panic errors started again. I tried different combinations of the RAM. The Apple RAM works fine by itself and the OWC RAM works fine by itself, but the only way I could get all 8GB of RAM to work was if I mixed and matched the Apple and OWC RAM (i.e. each row has one Apple stick and one OWC stick), but I thought it was best to have them installed in matched pairs. Everything has been running fine for a week, but I'm confused why they only work in that combination. I called OWC and they suggested they I run the Apple Hardware Test. I ran the extensive test last night and everything was fine. They also told me that the RAM I originally returned was fine. Anyone have any thoughts or suggestions? Should I be concerened that something isn't right with the iMac? Thanks in advance!!!