This error is likely caused by low disk space. Here's the deal: when PPro creates an FLV file it first creates a temporary uncompressed QuickTime MOV file, then uses QT to create the FLV. All this is done behind the scenes and is invisible to the user (however, if you want to watch it happen, open the export location in Windows Explorer and watch the MOV file being created). It's likely that when PPro is creating the huge uncompressed QT file that you run out of disk space and PPro throws the codec initialization error. It then deletes the MOV file and your disk space comes back to what appears to be a usable size. The other version of this problem that I heard is when your hard drive is formatted FAT32. PPro tries to write the temp QT file and once the file size reaches 4 GB, PPro freaks out and throws the error. If your drive is formatted FAT32, convert it to NTFS, otherwise export to a different drive or free up aditional space on your current drive.