BSAM - the ad blocking detection prompt is triggered if:
1) you are not registered
2) your ad click rate is very low
3) AND the ads are being blocked.
It is extremely highly unlikely for a false positive there. Most common blocking is by firewall software like Norton, ZoneAlarm and others, that have ad blocking built in, even if you may not be aware of it.
Other methods - some programs modify the Windows HOSTS file to screw up the IP address mapping for domains of ad servers. If you have a bunch of stuff in the hosts file, chances are that is causing the issue.