The most common and reoccurring cause of corrupt data is due to improper shutdowns of the CS1000 system. Pulling the power cord out or yanking a battery will likely result in a corruption of the CS1000 file structure, which often results in corrupt data.
The CS1000 software has been updated to better handle copying of potentially corrupt data, but severely corrupted media cannot be saved.
Sometimes USB drives can create problems. You can try to use a different USB drive or format the drive with FAT32 formatting.