How to prevent a PDO exception when using Rules to Set a data value after saving new content?
Have a look at issue # 430274, about an event which is a variation of your event here, and somehow explains that "after saving something" actually happens ... "before saving something" (which is not a bug, simply how the Rules module  works ...).

A possible compromise to avoid these kind of issues, is to transform what you're trying to do in your Rules Action (related to Set a data value) in a Rules Component, so that your Rule "schedules the execution" (using the Rules Scheduler submodule) of that Rules Component. For example after only a few seconds or minutes later on (if your cron job runs frequent enough, otherwise it'll be next time cron runs). This compromise will ensure that, at the time the Rules Component is executed, the "Save new content" for sure completed, and your new content will have been created as expected.

PS: I'm assuming this question is about D7.