Having read earlier posts on various forums, I was dubious about attempting to upgrade to I9100 XXKDJ. But I gave it a go and crashed and burned. Turned phone off removed and replaced battery. No harm done.

Removed and reinstalled Kies. Turned off PC firewall,fully charged the battery, removed all other USB devices except mouse and tried again.

After a long download period the phone showed the android symbol and
Downloading....
Do not turn off device.

This was the same message I got when it crashed. But this time there was a blue status bar beneath the text. and it was progressing!!!!

Next Installing Package details scrolled down the screen followed by an auto reboot of the phone.

A PC message then appeared saying disconnect then reconnect your device.

SUCCESS!!!!!

My phone now shows baseband version I9100XXKDJ


Hope this helps anyone who wants to tackle an upgrade via Kies.