I was having the same type of issue today while trying to resurrect a 3750V2 switch. I started by using TeraTerm and eventually went to HyperTerminal. Thanks to HyperTerminal, I was able to see a high percentage of retries. Looking back at TeraTerm, I was having the same type of issue but there was no indication from TeraTerm what the problem was. It would just stop part way through the file transfer. Based on some of the info in this thread, I was able to trace the problem to a USB to DB-9 serial adapter that I was using with my console cable. Switching to a RJ-45 to USB console cable eliminated all errors and the file is transferring as I type this.
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