So, I had the same problem as you. And the reason is FTP server FileZilla.
GT5 and RDR (for example) have files more than 4,5,6 GB, so when FTP programms tried to transfer it to my ps3 - it took too much time.
So after 5-6 minutes multiMAN or BlackBox (FTP servers on ps3) disconnected (or waiting/idle), so there was a fail.
I don't know how to solve this problem.
The problem is FAT32. How to separate files .vol and .rpf into files less than 4GB.