Apache Error log showing Pingback.ping error

Hi I have three websites running on an Amazon EC2 instance. All running 3.91 but I have had the same problems since early March so certainly was still a problem when I was running 3.8. Although prior to 5th of March I don’t think it was causing a problem.

https://www.ool.co.uk
https://www.oxfordhomeschooling.co.uk
https://www.writingschool.co.uk

My instance has been crashing every 7-10 days or sometimes more frequently. I suspect it is something to do with this reported error which seems to be getting more and more frequent. I think something like 50,000 times in the last week alone.

body.xml:1: parser warning : xmlParsePITarget: invalid name prefix 'xml'
<?xmlversion="1.0"?><methodCall><methodName>pingback.ping</methodName><params><p

This error is found in the apache error log.

I can’t find anything in code which would account for this.

Typically before the site falls over I get something like this in the Apache logs probably a dozen times over

[Tue Jun 03 07:16:28.288709 2014] [core:notice] [pid 3004] AH00052: child pid 11243 exit signal Segmentation fault (11)

I know that at the time, process 3004 was httpd so it is child of httpd but I don’t know why the fault.

The crashes don’t coincide with any event I can detect and don’t seem to correlate in anyway to network traffic. Although they do seem to generally correlate to periods of high CPU usage.

Any suggestions gratefully recieved as I am fed up of getting up at 2 in the morning to restart my site