Radius Server Dead

[WMA Hell]

I get these periodically during the day on the router syslog. 

Feb 16 19:33:22.817 EDT: %RADIUS-4-RADIUS_DEAD: RADIUS server x.x.x.x:1645,1646 is not responding.
Feb 16 19:33:22.817 EDT: %RADIUS-4-RADIUS_ALIVE: RADIUS server x.x.x.x:1645,1646 is being marked alive.

We have radius on a Windows Network Policy Server on two servers. CPU/Memory/Bandwidth are never more than 50% utilization.

Router#sh run | inc radius
ip radius source-interface GigabitEthernet0/0/0.x
radius server Salt
radius server Pepper

What does this tell me? How do I fix it?

[marce1000]

  - Check if the router has a solid network  connection to the radius server.
     + Check the radius server's logs when that happens . 

 M.