This is because that URL contains a temporary search ID that will expire after a few minutes.
For example, the search URL for all recent posts from a member looks something like this:
- toytowngermany.com/forum/?act=Search&searchid=21e52c611e83bf5f47075f80bfb1bea6&search_in=posts
That link might work for a few minutes, but after a while the search ID will expire.
To link, for example, all of someone's posts or topics, you should instead navigate to their profile, find the link that says "find members posts or topics", right click the chosen link, then copy and paste.
Wrongly posted search links are automatically redirected to the broken search link page after about 24 hours.