At some recent shoots, I've rented a 7D as video B-cam. During one shoot, when I transferred video files off the first card (which came with the rental - rated for video), only 2.1GB of data would transfer to the computer for two different files indicated as 3.98GB on the card. I tried to transfer these clips three different times to no avail - 2.1GB each try. When I transferred files off my own card next, the 3.98GB file transferred completely.
What could have been up with this to prevent it in the future? I rented the same camera previously without any issue.