Error in searching a thread

I tried to search the thread "Sid's Adventure Jounral" for bounty hunter, and a page came up with the following error:

vB_Legacy_User does not have a field 'username' on line 40 in /var/www/html/webroot/uk/forum/vb/legacy/dataobject.php
#0 /var/www/html/webroot/uk/forum/packages/vbforum/search/result/post.php(145): vB_Legacy_Dataobject->get_field('username')
#1 /var/www/html/webroot/uk/forum/vb/search/resultsview.php(122): vBForum_Search_Result_Post->render(Object(vB_Legacy_CurrentUser), Object(vB_Search_Criteria))
#2 /var/www/html/webroot/uk/forum/vb/search/resultsview.php(186): vb_Search_Resultsview->render_searchbits(Array)
#3 /var/www/html/webroot/uk/forum/search.php(394): vb_Search_Resultsview->showpage(0, NULL, 'search.php?sear...', Array)
#4 {main}
Fatal error: vB_Legacy_User does not have a field 'username' on line 40 in [path]/vb/legacy/dataobject.php in [path]/vb/vb.php on line 287

Does anyone have basic info about the "Bounty Hunter" Adventure?