Chronic DAE-9128, -6030, -6097 or others in ProTools LE 6 and 7 on Mac OSX. Even playback on simpler sessions is halted.
We've encountered a few cases where third party, seemingly unrelated hardware is the cause. First, check the usual.
1) System preferences, like Energy Saver, Security, Accounts (login items), etc.
2) Check Mac HD/Library/Startup Items for anything other than Digi and PACE stuff
3) Disable Airport and Bluetooth
4) Trash preferences
5) Update PTLE (including CS updates) and make sure OS is compatible.
If problems persist, find out what other hardware is connected. USB hubs, printers, other USB hardware, FW hubs, FW expansion cards? PCI cards? Try removing any variables.