Error when bouncing to disk

[Helge Krabye]

I am struggling with setting up ProTools 10.3.3 to bounce my 60 minute long Session (four stereo tracks, two eq filters, one simple delay) to disk. After about twenty minutes, the error message "could not read audio fast enough from hard drive" (or something similar) pops up. I have tried different settings in the Playback Engine without luck. I have the fastest ever Mac (2012 model iMac 27" 3,4 GHz i7 with 16 Gb RAM connected to a fast Firewire 800 external hard drive). I never have this problem when bouncing in LogicPro and Live8/9. Is it normal to have this problem with ProTools 10? Where can I find a guide to set up my system correctly? By the way, I bounce to my internal harddrive (desktop), while the Session and all audio files are on the external Firewire-drive.