You can respond to requests in Hire a Freelancer/Want to Buy, even with violations. However, you're not allowed to advertise your services outside of these sub-forums. To submit a market place thread, you need to be violation free. In your case, you can wait the 2 weeks until it expires, or you can contact the original moderator that gave you the violation to see if they will remove it. This is completely at the discretion of the moderator who gave you the warning originally.