Many poeple struggling with updating their ps3 key.
I found following solution, unfortunately only working for the silabs based stickies (darg and drop allowed)

I was struggling with win 7 for 3 days.
Noticed after i added my serial on the PS3 key website mine was silabs based so drag and drop should work but even that didn't work.

Then i was thinking lets try in ubuntu (dual boot laptop).
Mounted the usb stick (nicely recognized as ps3 key in dmesg)
did a simple cp firmware.bin /media/mountpointusbstik

and volia it worked.

This tells me it has to do with admin or other privileges within windows 7.
So if you have a friend or maybe yourself with ubuntu installed that will work but again only for the silabs based sticks.

Have fun all.