It works fine. I just made a video of the process last week so you can watch and see if there are any differences to what you are doing if you want: Creating a signed FileMaker Runtime and installer package for OSX - YouTube
It seems like your FileMaker data file (.fmp12) doesn't have write permissions, do you have the file open in server, or do you have the file open by another copy of FileMaker pro? Do the permissions in Finders "get info" say that you have write permissions? Make sure that the file is closed before making the runtime.
It may be an issue with Info.plist file being read only for non admin accounts on the Mac. See the following help file
Thank you very much for your advise. I uninstalled File Maker Pro Advanced and installed it again. After this, I could have my run time running with no problems.