Try formatting your flash drive so that it's in the "NTFS" format. You should be able to do this very easily. This may solve your problem. Read the instructions to see what the format currently is. It may be that your flash drive is formatted as "FAT32" and not "NTFS".
If it's formatted as FAT32, then this may be why you aren't able to copy the 8GB video file.
Hope this helps.