Okay, I'm a total Mac guy, but audio stuff is a bit beyond me. Now my uncle has upgraded to a Mac Pro (8x 2.8 GHz, 4 GB RAM, etc). Randomly he would get an error when using Pro Tools. There are a couple of them that seem to be randomly chosen. This is one of them: Code: The operating system held off interrupts for too long. If this occurs frequently, try increasing the "H/W Buffer Size" in the Playback Engine Panel. (-6086) Obviously speed is not the issue. I thought tracked it down to Guitar Rig 3 which does not support working as a plug-in with Pro Tools and Leopard. Removed the plug and it came back. We did a total wipe and with a fresh install Pro Tools was working perfectly with Reason and it happened again. No GR3 installed. Yes I have patched to the newest versions. Pro Tools 7.4.2 and Reason 4.0.1 (if I recall). Both Reason and Pro Tools are supposedly fully supported under Leopard (up to and including 10.5.4). Does anyone have any idea why this is happening? Mac Pro 8x 2.8 GHz Leopard 10.5.4 (we did the same testing under 10.5.2 and 10.5.3) Pro Tools 7.4.2 Reason 4.0.1 Digirack 002 via FireWire We did install another plug-in (forgot the name), I have him testing it out without that plug-in installed just in case that's the cause as we did it last minute and didn't test with it. But it's a minor one. PS I can get any more detail you need such as the exact error code, etc. I've Googled like crazy and it looks like I'm going to need help.