It happens when burning a video disk/DVD. I have had the error when burning several short videos to play in succession, as well as a single large 1 hour video. It has happened only with Toast, both v12 and now v14. Rebooting hasn't made a difference. Running OS 10.8.5. Toast will encode or multiplex, and begin the burn. Toward the end of the burn comes the error message, and the session must be cancelled. I turn off all other processes except Finder to give the max to Toast. The computer is a late 2010 Macbook Pro, 2.66 GHz processor, 16 GB memory. Have replaced the DVD internal player with a 1T harddrive. Startup harddrive is a 1T SSD.