Yes most of the failed renders were to hard drive. I've tried switching between the external hard drive (FAT) and the internal one (NTFS) in the hope that maybe it was some sort of hard drive issue to no avail.

When you render to Blu-Ray I believe it renders the image to a file on disc before burning the Blu-Ray anyway so reference to Blu-Ray is a bit of a red herring.

I have a new show to put together this weekend so it will be interesting to see if I have the same problems or if this is a one off with the project I have been using.