After Effects question.

I’m exporting a test of an opening sequence that I’m building in AE. I go to export a low res test by adding to the render queue like I always do. It gets about 3/4 of the way done, and then gives me an error that there is not enough disk space. I am using an external hard drive that has about 26 gig left, and this thing should only be about 5 gig. The only thing I could think of is maybe AE needs a contiguous section of HD space and the drive was too fragmented and didn’t have enough space, but I defrag and it’s still doing it. I haven’t tried outputting to the native HD, but I’ll try that next. With each experiment taking about 20 minutes, I’m tired of wasting time. Any suggestions?