A mismatch in speed and duplex settings can lead to CRC errors because it creates a situation where the transmission and reception of data packets are not properly synchronized, leading to frames that are not correctly formed, thus generating CRC errors. Hardware and transmission media integrity have been confirmed to not be the issue, hence the administrator should look into the configuration settings for speed and duplex to ensure they are correctly set. Electromagnetic interference would more likely cause packet loss rather than CRC errors. A software update for the switch causing CRC errors is unlikely unless it pertained directly to physical layer operations or port configurations, which is not suggested by the elevated CRC error count alone.