Hi, I had a really hard time with this. Uninstalled, reinstalled, external hard drive, internal, copied and pasted into a new sequence… nothing worked. What was strange is that the playback wouldn’t work on my iMac (osX 6.8) but it would on my laptop (same os) so I didn’t upgrade to osX7. I also could not find the plist file when I did a spotlight search but when I manually went into the Preferences folder I found it. HD>username>Library>Preferences
After deleting the plist file, the playback issue fixed itself and it’s been running fine all day. I am using Premiere Pro 6.0 from Creative Cloud as a Trial version, no updates.
I joined this forum hoping I could help somebody, this was a tough one.