"USB error..." using inst track for first time

[SIM1]

Been using PT for awhile, recently moved to 7.0 on my brand new G5 Dual. Yesterday, whil working on a project that only has one audio track (ac gtr with no plugs), I opened MOTU Symphony on an instrument track and all of a sudden started getting some "USB error......check buffer in PLayback Engine" (sorry, not at computer now). ANyway, I opened the system usage window and did not see much going on (there is no way I am pushing the limit as I have done much larger projects). HW Buffer set at 1024. What else should I look for or is there maybe a patch or something related to Inst Track. Never had this issue when doing the Midi/Aux combo?

All help appreciated and will be searching the forums as well.