Fatal errors tend to cause problems with the instance and normally you want to fix these errors because of this.
I dont recognise the relationship that it is looking for, have you any plugins installed ? have you tried repairing the relationships using the admin panel ?
I have done a bit of digging and I can see the error now. I will look around a bit more and see if i can work out what is missing. I will update you if I get to the bottom of this.
I wouldnt worry as this appears to not cause any issues in any way.