Most likely the query dispatcher does not find the right query and tries to execute the inline one in the index.tcl file, which does not work.
Did you try modifying the lines in the .xql file:
<fullquery name="dbqd.www.index.user_name_select">
to something like this:
<fullquery name="dbqd.www.subsite.index.user_name_select">
There was a bug in the query dispatcher related to this some time ago, which may still be there, but you should try that at least.
