That can not be the cause in my case and most likely many others.
As the memory I was is 1066. I confirmed this by installing them into a pc laptop and using cpu-z and the SPD table list the maximum speed as 533mhz.
And that both ttuuxxeerr and myself had problems with 2x 4GB in the mac mini and finally got it to work.
Also as for the other mac mini server I upgraded.
The firmware had already been updated.
Before shutting down the mac mini for the upgrade I ran 'sudo nvram -c' in terminal.
Rebooted, Did a single PRAM reset and forced power off by holding in the power button before it booted again.
Installed the ram upgrade, then powered back up, Did a single PRAM reset.
BINGO IT BOOTED FIRST TIME 😀
But Yes I do agree buy quality ram with a lifetime warranty ( if the manufacturer does not trust the quality of their product why should you ).
And buy the correct speed, Although higher spec should and usually does work. Some mac's are very fussy and if the matching speed for that model have not been programmed into the ram's spd table it will not work no matter what you do.