spinning wheel (freeze) when pressing play

[anricat]

I just upgraded to Leopard (10.5.4) and ProTools 7.4.2cs4. Now, whenever I press play in any session (new or old), I get a SPOD (spinning wheel of doom) and I have to force quit. If I have audio in my session, it always happens. If it just have software instruments, it's fine and plays without issue. If the audio file is very small/short, it plays for a second or two and then I get the SPOD and I have to force quit.

I have a Mac Pro dual 2.66 GHz and 2 GB of RAM (I know, I could use a bit more RAM). I'm recording on to a second internal drive (but I've also tried my boot drive just for the heck of it - same issue).

I've removed all my plug-ins, repaired permissions, and deleted all pref files.

I'm totally out of ideas.