Video clips won't render

[heagneypr]

Has anyone experienced a problem with video clips that won't render? Although the clip in question has been rendered several times during the creation of a project, it suddenly hangs up during the rendering process. The only way around it is to pull the clip, re-render it in h264 (instead of MP4), replace the clip in the time line with the re-rendered clip and ... voila! ... it works. Any insights as to why this happens in the first place?