Most likely cause is that the Qlikview document has section access applied and the publisher service account is not permitted access. If the access security is using NTNAME, make sure the publisher service is listed in the section access table. If the access security is via USERID/PASSWORD, then enable the Section Access checkbox and enter the USERID and password values in the QMC task.
Either the NTNAME or USERID must have ADMIN level access, not USER level access.
QlikView Publisher assumes that the account running the QlikView services in Windows (check Run > services.msc) is included with full access in the section access table, therefore you don't need to add anything.
However, if you are not using NTNAME or you don't want to / can have the service account added, you need to manually specify the USERID, PASSWORD pair with admin permissions to be able to open and reload the document with all the data.