8315 Error in Project Server 2013

Hey all,

My Project 2013 server just recently started throwing an 8315 error. Its details are:

Machine 'NTPRJWEB2 (SharePoint - 80(_LM_W3SVC_1989583194_ROOT))' failed ping validation and has been unavailable since '6/18/2014 2:27:52 PM'.

and:

Machine 'NTPRJWEB1 (SharePoint - 80(_LM_W3SVC_1989583194_ROOT))' failed ping validation and has been unavailable since '6/18/2014 2:27:49 PM'.

I have never had to deal with this error before. Can some one advise me what I need to do to resolve this?

Thanks,

Jonathan