An error occured when provisioning a new custom site definition with custom features.
No useful logging information or error messages other than the line:
Failed to instantiate file “default.master” from module “DefaultMasterPage”: Source path “default.master” not found.
Problem was a custom feature with an activation dependency. In the process of trying to set it to a hidden feature, I forgot that you can’t hide a feature with an activation dependency. Hence it was throwing an error.
So in short it was a real pain to debug, as you can see the MS error message is absolutely useless!