I just tried searching as a guest and got no db errors of any kind. It is working as designed. I did, however, update this hack as it was not showing Guest as the searchee name when a guest had searched.
@ TundraSoul - Try uploading a fresh search.php and enabling this product and see if maybe something else is going on with it. If you have guests set to not be able to view forums, turn the searching off as it will not do them any good anyways.
I cannot reproduce the problem you are having, sorry.