Sfp Current TX RX power is below low boundary. Current value is 0 uW mA

Hello,   In the show logging raslog and in the Master Log of BNA, now and then there are entries like this: 2013/08/12-00:02:35, [FW-1038], 78695,, WARNING, switchname, Sfp RX power for port 31/0/49, is below low boundary(High=1000, Low=32).