I found the problem cause :-) Thanks, for eliminating PHP as a potential issue.
This is still an issue, but certainly not PHP or server issue. I was running Norton security on the client and apparently Norton was doing the blocking. I disabled Norton security and the ad is no longing commented out. I re-enable Norton and the ad gets blocked. I had no idea Norton was getting into the packets and doing anything else than just blocking URLs (by looking at the packet header).
I suggest that the "/ad/" string is replaced with something more dynamic. Certainly changing it to "/add/" helps.
Again thanks for everyone's help.
Mark