Have you agreed to use the OGL or d20 licenses? If you haven't, then you aren't bound to them. A contract that has not been accepted is not enforceable.
In the OGL it states that by using OGC, you agree to the OGL. Are you using OGC? If not, then the OGL doesn't mean anything to you.
Did you send in the d20 card and start using the d20 logo? If not, then you aren't bound by the d20 license either.
IIRC, nothing in the FRCS is OGC. In the copyright notice on the first printed page of the FRCS it states that WotC claims as a Trademark all "Wizards characters, character names, and distinctive likenesses thereof ...". I don't know if such a blanket claim is legally enforcable or not, but let's assume it is until otherwise proven.
So if you wish to publish your adventure which is in FR, you simply must not duplicate any copyrighted material. If you reference any trademarks (ie. "Wizards characters, character names, and distinctive likenesses thereof") then you must put (tm) next to that, and in a footnote declare that this is a trademark owned by WotC. Other than that, why can't you put your adventure on the web?
Be sure and put a page in front of the adventure with a link to the adventure that can only be gotten to by agreeing to your "terms and conditions". In that, make sure you say something to the effect of "by agreeing to these terms, you agree that the place of publication of this adventure is <your_home_town> and is bound by the laws therein, and any litigation regarding this will be done in <your_home_town>." Because if you don't, they can file a lawsuit against you in their city, and if you don't show up to court to defend yourself, you automatically loose. Since they know most people won't spend the money to fight a lawsuit in another city, they automatically win anything they feel like, even if their claim is baseless. If they serve you with a "cease and desist letter", then file a lawsuit against them immediately (in your city) to prevent them from baselessly harassing you. Then they can either fight that lawsuit (which may be just a bluff, but they don't know that) at considerable expense, or compromise and allow your adventure to sit where it is. Hiring an attorney to file the lawsuit for you shouldn't cost a whole lot. Or just file it in small claims court for like $20. Actually litigating a case may cost a bunch, but I'm not saying that you should spend that much money.
If everytime someone receives a C&D letter, they immediately respond with a lawsuit, perhaps they will slow down the printer speed on those damn C&D letters.
Anyway, this is just my opinion based on my very limited understanding of the law, so consult a lawyer before you do anything.