It usually happens when there's a link from one forum thread to another. I don't know why, but the relative links are kinda screwy. If you want to, you can get around it though. I'll give you an example:
(Note: I put the URLs in italics so you can identify where they start/end more easily. Edit: I also colored them.)
From the Modding section there's a post called "[INDEX] - Conversion Projects (consolidated)" https://forums.sinsofasolarempire.com/174340 which has links to the popular conversion mods. The Stargate mod link doesn't work. The link should be https://forums.sinsofasolarempire.com/177748. However, the forum gives you a link to https://forums.sinsofasolarempire.com/174340?forumid=443&aid=177748. Ugh. If you look at it, though, you can see the original thread's number 174340 and the linked thread's number 177748. If you delete the extra crud aside from the number of the thread you're going to (in this case, the 174340?forumid=443&aid= part), it will give you the basic URL for the thread https://forums.sinsofasolarempire.com/177748, and you can get where you want.
It's still annoying, to be sure. At least you can get there now. ;p
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