[Freesteyelz]

Open your threadbit template and click on the "Show Default" at the left. When comparing your template and the default's template look for the following lines:

			<if condition="$show['guestuser']">
				$thread[postusername]
			<else />
				<span style="cursor:pointer" onclick="window.open('member.php?$session[sessionurl]u=$thread[postuserid]')">$thread[postusername]</span>
			</if>

If it's missing or has been modified in your current template re-add them.