While doing configuration of DLP section, Restart SafeSquid service twice if it is a fresh installation of SafeSquid Appliance Builder (SAB).
When the activation of SafeSquid Appliance Builder (SAB) is done, Restart SafeSquid Service prompt should appear on SafeSquid UI. After Restarting SafeSquid service lib-magic library file still doesn't exist, which you can verify from SafeSquid logs. To obtained the status 'libmagic: ok' you have to Restart SafeSquid Service once again from SafeSquid Interface.