Pete,
The best I can suggest is to re-install JomSocial. All your settings should remain intact. If the version information is missing there, then it's possible other aspects of the installation didn't fully complete as well, which re-installing should fix as well. If you've made any modifications to their code, they would be overwritten, so be careful of that.. but generally you shouldn't be modifying their code directly.
I hope that helps, but if that's not possible or doesn't work, we can help force the JomSocial social profile plugin to install through alternative methods.
Thanks,
Alex