Soft parity errors - These occur when an energy level within the chip (a one or a zero, for example) changes. When referenced by the CPU, these errors cause the system to crash if the error is in an area that is not recoverable. In case of a soft parity error, there is no need to swap the board or any of the components.
Hard parity errors - These occur when there is a chip or board failure that causes data to be corrupted (not bad all or most of the time). In this case, re-seat or replace the affected component, usually a memory chip swap or a board swap.
Studies have shown that soft parity errors are 10 to 100 times more frequent than hard parity errors. Therefore, waiting for a second parity error before replacing anything is highly recommended, as it greatly reduces the impact on your network.