Hi Gaby, check out some of this points, probably is one of them:
1. Make sure the user you are logged in is in your section access list.
2. If you are using NTNAME and you are out of Domain, make sure that your OSUser is equivalent to the QVUser in your section Access.
3. Check out internal security in the File, probably there are conditions in all sheets to denied access to some users, go to Settings/Document Properties and go to Sheets tab to check if probably all sheets and hidden to the user you are using.