it seems that the search function works well under the site.com/forum/ but when you move to a different place like site.com/wiki/ and do a search from there, it will return error.
I tried to search in the top level domain site.com/ and it returns something like this
http://www.site.com/ 67.86.193.xxx /ajax_search.php?query=and
www.site.com Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.3) Gecko/2008092417 Firefox/3.0.3 (.NET CLR 3.5.30729) 404 Please contact admin if you can not find the content you are looking for.
This should be easy by using relative path instead of absolute path?