Hello Xume, I am also facing the same problem!
Kies was working fine for two months and after an update to JH1 for 8500, could not upgrade to JK1 (INDIA).
that error was MSC Thunder stopped working, ( found the solution in this forum)
But now after repeat reinstallation and using the cleanup solution also, phone is not connecting on usb to kies. Tried bluetooth connection and it did connect. I guess this is some incompatibility issue with win7 64 bit usb drivers.
have contacted samsung customer suppport, lets see if they have a solution.
Your help would be appreciated.
Tinkered with trobleshoot compatability options after right click on kies icon on desktop.
click and option list appears.
does not resolve with xp frame but if you "run as administrator", the PHONE DOES CONNECT. I AM ECSTATIC.