Code signing! Where are the certificates stored? & Running other peoples source code

Hi

I am trying to run someone else's source code on my device but I am constantly getting this error message no matter what I do:

Checking Dependencies
Code Sign error: The identity 'iPhone Developer: FirstName LastName' doesn't match any valid certificate/private key pair in the default keychain

Yes I am an iphone dev member, I have made a new provisioning file and changed the provisioning settings. I have submitted an app and done this before! My certificates/private key are there.

So It somehow knows the name of the developer who created the source, where is it storing this information? I have changed the settings so that it points to the provisioning file with my name, but still it shows up the name of the owner. I've grepped the source but no sign of the guys name.