Problem with RAM Upgrade

Hi,

I happened to have two 2GB RAM Chips from my new 2012 MacBook Pro (which was upgraded to 8GB) and wanted to use them to upgrade the older 2009 MacBook Pro, which runs with two 1GB Chips.

Unfortunately, the MacBook won't start after I have installed them. Back with the old Chips it is running fine again.

The specification of the two new Chips is 1Rx8 PC3-12800S-11-10-B2. The old Chips are already inside the Mac again, so i can't tell their specification right now, but it was obviously different.

Why shouldn't they work? Of course they are supposed to run with much faster FSB than the old ones, but running slower shouldn't matter? Or is there another difference in the specification?

Thanks for your help, the old MacBook would really like the Upgrade ;)