it most likely has nothing to do with the WLC, but the PI appliance (hardware).
the PI appliance is based on a UCS server hardware platform and as such also has a dedicated management processor (IMC)
the imc checks the hardware and forwarded this message to PI log.
Iy you have physical access to the appliance, you could connect the IMC network adapter, login to the IMC and view detailed hardware info and events. (and clear the event if necessary)
if this only occured once, it could be only cosmetic.
