Hi Francisco,
I believe you are opening the wrong URL to access the Query Builder.
If you are using BI 4.X then you have to access it using http://<servername>:<port>/AdminTools so according to your url it should be http://WEBAPPServerName:Port/AdminTools .
Also if you can check the below articles for the queries : BusinessObjects Query builder queries
Please let me know if you are using any other version of BI or Still getting the same error when accessing the url.
Hope this will help you.
Regards,
Mahak