I used to have that problem on the WT41N0.
You will need to install the cab file for SQL Compact 3.5.
Look in Program Files/Microsoft SQL Compact Edition/3.5/Devices/Client/wce500/armv4i
Copy sql.wce5.armv4i.cab to your device Application storage area and modify your startupctl onRestore script so it has the following lines
\windows\wceload.exe /delete 0 "\Application\sql.wce5.armv4i.CAB"
You will need to install StartUpCtl on the device.
I have installed the sql.wce5.armv4i.CAB from "C:\Program Files (x86)\Microsoft SQL Server Compact Edition\v3.5\Devices\Client\wce500\armv4i".
The dbnetlib.ddl error doesn't shows, but the Sql server connection doesn't run.
The WT41 terminal shows an sqlexception.
The Sql server database is correct becasue the ols terminal WT40 connect succesfully.
Do you have any comments more?
Thanks in advance for your collaboration.