Unexplained errors 403

In the past two months, we've noticed that some visitors to our website receive 403 errors when accessing certain php scripts. Specifically, there are exactly 4 IP addresses up to now, which is a coincidence (or not) for the 4 addresses in Norway. Hundreds of daily accesses to the same scripts of other IPs work perfectly. We searched all the .htacess files and the various security and firewall components and there is nothing …

Unexplained errors 403