Have you tried Audio Mixdown? Also, you might try using Render Manager to delete audio renders, and then re-render. What’s your I/O card or box? Where’s your media stored? How much space is left on that drive? Also, audio needs to be 48k 16 or 24 bit, not 96k. Also, I’d run Disk Warrior.
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
ATTO ExpressSAS R380 RAID Adapter, PDE Enclosure with 8-drive 6TB RAID 5
24″ TV-Logic Monitor
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