one of my RAM sticks causes a Kernel Panic on my Ubuntu 10.10 (something like not syncing with a lot of memory adresses shown on screen). It's definitely this one RAM stick and not its socket because when I put one of the other sticks into the slot of the one RAM stick, everything is ok. How does it come that memtest doesn't find any errors after several cycles but Ubuntu is not able to boot while using this one special RAM stick? Does anybody have an explanation for that? 
Kernel Panic because of RAM stick?
ubuntu;memory;kernel panic
What is several passes? What memtest tests have you run? I know I have seen memtest86+ take up to 6 or 7 passes to find an error with RAM sticks. Also, make sure you run the full battery of tests.It certainly does sound like the RAM is bad. I too have had not syncing panics because of bad RAM.