Losing wifi settings in keychain

Hello all,

For some reason, approximately once a month, the Mac loses the wifi settings. This sends the clock back to January 1st and takes several attempts of reentering the network name and password before it is recognised again.

Also, the wifi settings seem to no longer be part of the keychain when that happens.

This is getting to be a pain. Does anyone know why this happens (it only happens on one of the Macs; others are fine)? What can I do to repair it for good?

Thanks,

 

Does nobody know?
Is it maybe a plist which needs deleting or is there a way to stop the keychain deleting the wifi settings?