I recently upgraded my RAM and keep getting a prompt that my module are placed incorrectly, plus some of them are not recognized at all. I have a Mac Pro 2x2.4 GHz quad core and the following RAM modules: 2 x 8GB OWC sticks 2 x 4GB OWC sticks 4 x 1GB original ones that came with the computer. I would like to know two things: 1. What is the ideal configuration with all sticks? 2. In case slot 1 is defective (which it might be) what would be the best scenario then? Just to avoid confusion, please provide in your answer the slot numbers (1-8) in which the memory needs to be installed in. Thank you very much for your help.