I did try same sizes in 1-3 and 2-4. Any time there is a stick in slots 3 or 4 I get the debug lights.
I just tried updating my BIOS and that didn't fix it. I thought it might because a few of the updates said better memory compatibility, but it didn't.
The issue seems to be slots 3 and 4, not the memory, because both of them work when in slots 1 and 2.
Just want to be sure, you had just you old ram moved to slots 3 and 4 and nothing else in and it still bugged out?