I know this is an old thread, but this is the first result in Google for
"x-httpd-php5 returned invalid result code 70007"
After spending 2 days troubleshooting this issue, including moving to another hosting server, I've found what was the culprit for at least my problem.
I was using a firewall with a web proxy to access my sites.
with the proxy turned on, I would get this sporadic "x-httpd-php5 returned invalid result code 70007" in the apache logs. Only as a last resort I even thought to turn off the proxy on my end - since it's never really given me any problems - and the error could no longer be reproduced. I've posted this on the firewall developer's website - but I going to just put in an exception to not proxy this IP address as a quick fix.
Just thought I'd post this in case anyone else is still having this issue and hasn't considered the problem may be caused by the machine accessing the website.