yes I was using Internet-ID connection, but tried both ways and neither established connection.
Meanwhile, I had the logs disabled. Before I enabled them I gave another shot and uninstalled RU again, cleaned temp files and reinstalled RU on 1 of the XP machines. It's working now.
I'll try to do the same to the others, but I find a bit strange that this happened only on XP machines, and always after upgrading to 6.9
Anyway, thank you for the support! :)