As far as I know there is no certified Navision connector, as it does the SAP one. Native Navision flow fields (for example) are not accesible via the SQL Management Studio or the ODBC or OLEDB drivers. So you will need to find out what the flow field within Navision does in order to replicate the same logic in the QlikView document (usually the load part). Same with some tables that are calculated run time in Navision, and stored using VSIFTs or some other Microsoft proprietary technology.
Let's see anyway if some people has got it other way.
Do you mean you can run some sql statements in the query analyzer or the management studio and they run fine but you cannot when you connect with QlikView?
If Navision is installed over SQL Server, any sql statement you do will work in QlikView as well. If it's installed with itsnative database format, you can try with their native ODBC if you have it (it's a different license, but check this with your Microsoft sales rep in any case).
You only need read permissions if you are only going to run SELECT queries.
In addition, I'd use an OLE DB connection rather than the ODBC, unless you are using the native Navision driver.