Secured web with unauthenticated users accessing a service

hi all,
I have a following configuration:
~/ui/login.aspx, ~/ui/page1.aspx, ~/service/main.asmx
access to web is secured using:
<authentication mode="Forms">
  <forms loginUrl="~/ui/login.aspx" timeout="10" />
</authentication>
<authorization>
<deny users="?" />
</authorization>
 
but I want to allow unauthenticated users to issue (possibly limited set of) a query to the service (e.g. to display service version on the login page using service call ~/service/main.asmx/GetFullVersion). I'm able to do it locally, but on the server there is a problem and the service cannot be queried. I tried to set
  <location path="~/service/main.asmx/GetFullVersion">
<system.web>
<authorization>
<allow users="*"/>
</auth ...