I'm having the same issue. It seems to be a 10.6.8 issue based on what I'm hearing from you guys... I have a show on Friday and I'm about to not have midi tracks for it... very very bad......
Also, I have not been able to get it to play back at all.
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MacBook 13" 2.2 GHz Intel Core 2 Duo
2 GB ram, 500GB Hard disk
OSX 10.6.8
ProTools 9.0.5