I managed to get some more detailed information:
Module FastCgiModule
Notification ExecuteRequestHandler
Handler PHP55_via_FastCGI
Error Code 0x800704e7
Requested URL http://xxx.xx.x.xx:80/moodle/backup/restore.php
Physical Path \moodle\backup\restore.php
Logon Method Anonymous
Logon User Anonymous
I will continue investigating but if anyone else can shed any light, please do.