Is it the standard premiere titler your using?
Is there any other effect on the actual titles?
What format are the titles being saved as?

Ive only ever seen this before when there was no media on the track below so these are just ideas!

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Full Specs: 3.2 Pentium 4 Processor, 1Gb RAM 80Gb Root Drive, 120Gb Video Drive + another 160Gb external, Adobe Premiere Pro, Pinnacle liquid edition pro, ati radion 256mb