I have a 92 minute sequence, shot in HD, that I'm trying to export as a QT movie. I have 34 GB of space on my hard drive and, yet, I'm getting the error message. Is it possible it needs more than 34 GB or could there be another cause?
First, you haven't mentioned what codec you're trying to export to, so calculating the disk space required cannot be done.
And, you must always consider the following factors when you fill a drive so close to total capacity.
1) Whenever exporting a file, a temp file is written first, and that essentially means that you need the space for two files, not just one.
2) The empty space is not contiguous, especially when nearly full, it's instead tiny tracts of empty space that the OS must find and write to individually, thus slowing the process to a comparative crawl.
Most here export a self contained file first, then use that as a master to create web delivery files and MPEG2 encodes for DVDs. It's much quicker, and less prone to issues. You should do that too, but first clear some space on that drive or get a new one.