We solved this issue.
After stuffing around with certificates for days we resolved this by stripping things right back to essentials.
- compiled basic hello world in pure xcode and it distributed
- compiled basic hello world in titanium and it distributed
so we could rule out the certificates, xcode and titanium, it must have been a problem with the project. We would have done this sooner but the projects had previously compiled and it really looked at the time like it was a certificate issue.
solution: it turned out that there was an extra Info.plist file in our titanium /resources directory that was now out of date (possibly referencing old certificates?) and overwriting the one in the titanium /build folder, once we deleted the Info.plist, cleaned and rebuilt the project everything was sweet again.