I understand that the Core extension is installed by default for all new web properties. We have noticed that the build fails when building the library for new web property for the 1st time after creating the 1st rule that uses Core ext.
To work around this issue, you need to disable then enable Core extension (only once and then all builds for all libraries will work fine as long as you dont have other issues). We hope to have a permanent fix for this instead of doing the work around
Thanks for sharing, worked for me! I was already getting very nervous because I could not bulk publish anything...always had to go to each and every Rule/Data Element and click on "Save & Build".
Btw: the bug is not only on new Web Properties, it affects as well old ones.