Ok, that additional info from you may have help me not sound so "harsh" if you had put it in your first post. It's always best to give as much background info as possible from the start.
So you say you have set the blocking cookie for 3 projects and it blocks for 2 but still don't block on one of them? That sounds odd. Is it always the same project that are not blocked. When you set the blocking cookie, do you set it for all 3 with one click from the "My Projects" page? Or do you go to each project and block one at the time separately?
Try to unblock all projects, one by one to start with. Also delete all cookies from the browser so you start "clean". Then block all projects, all together from the link on "My Project" page. Then go to each project and check if the cookie is blocked. If one (same) project still is not blocked, I can only advice you to post a support ticked so the tech guys can take a look at it.