I have a Vaio FRV37 laptop which is expandable to 1G. Ram.
( originally 512MB/ 2-256 PC 2100 cards.)
I added 2- 512 cards and comp. gives blue error screen just after boot up.
I then took out (1) 512 strip and put back a 256 strip, now leaving one strip 512mb, and the other strip 256mb, and comp. works fine.
Anyone have a guess on what I need to do to make both 512mb strips work ?
Thanks!

With the 512 and 256 in place does it recognize all the RAM? If so, try swapping the sticks in the slots. If that doesn't work, check with Sony.

I did the swap test as you recommended, and think I found the prob.
Switching what was already in the slots made no difference, (comp. also recognized both cards OK.) but when I swapped the 512mb card with the other 512mb card, I got the blue screen.
Im guessing that one of my 512 cards is broken?

Sounds like it

That stinks.
Thanks for the help, though!