community.tacticsoft.net and tacticsoft.discoursehosting.net are actually 2 separate domains of the same site. You are most likely logging into the community site and so when you click a link that uses the other domain, it considers you not logged in. I find it weird but I am sure @Alexander has a good explanation for why discourse has our forums like this.
Edit: the tacticsoft site is https while the other is not. Never noticed that before.
You can use the same login details on the other linked site as well.