RESULT!
I paid for the hosted server. Deleted all the old files from the keys folder and started again following the tutorial for the creation of certificates and provisioning profiles, while doing the whole thing on the Windows machine running in Parallels on the Macbook.
I un-installed B4i-Bridge, recompiled it in B4i via the hosted server, installed it again on my iphone, and everything is working now.
I use the Hosted Server from inside B4i, and the bridge installs my code.
Meanwhile, X-Code works quite happily with the certificates and profiles that I have set up for that on the Macbook.
Very, very pleased and impressed with B4i!
Thanks Erel.