This item is from the Yet Another Enhanced IDE/Fast-ATA/ATA-2 FAQ, by John Wehman and Peter den Haan with numerous contributions by others. (v1.92).
Often, this is caused by the use of block mode (see Q10.6 for an explanation). Large blocks can take a long time to transfer; during the transfer, interrupts are disabled and the serial ports are not serviced by the CPU. Eventually, the buffer for incoming data may overflow, leading to overruns and CRC errors.
The solution is to reduce the number of sectors per block, if possible, or disabling block mode altogether. 16550 compatible serial ports have a larger buffer, but with excessively large block sizes this problem may still occur.