You could have a bad render or media file. First, trash prefs and repair permissions. If that doesn’t help, use the Render Manager to remove the current renders from your project and then re-render. If that doesn’t work, to find bad media, you want to narrow down where the bad media is in the program. First, export the first half of the program to h.264. If that doesn’t work, break that portion in half and export. If it works, the probem’s in the other half. You keep narrowing down until you find the bad media. This is a pain, so hopefully, one of the earlier methods fixes the problem.
John
MacPro 8-core 2.8GHz 8 GB RAM OS 10.5.5 QT7.5.5 Kona 3 Dual Cinema 23 ATI Radeon HD 3870, 24″ TV-Logic Monitor
ATTO ExpressSAS R380 RAID Adapter, PDE Enclosure with 8-drive 6TB RAID 5
Final Cut Studio 2 (up to date)
Pro Tools HD w SYNC IO, Yamaha DM1000, Millennia Media HV-3C, Neumann U87, Schoeps Mk41 mics, Genelec Monitors, PrimaLT ISDN