I have my Dell Vostro A90 runing 10.6.4 again.
I solved something...but still a dash of mystery remains. See the attached picture.
The 64 Gb Runcore SSD
is not as "thick" as the original one supplied by Dell. It wants to be seated in a crooked way.
And there is an issue with one of the screws. I think due to the skewed seating, the screw touches a component on the board and it may cause a grounding problem. I originally thought that tightening the screw might be flexing the board and causing a pin to lose contact, but even when I lightly tightened it, the SSD
was not detected by the BIOS. I might try to find a nylon screw or try putting teflon tape on the provided screw.