DPA 5 Code 39 Driver Error (NcBulk.sys) – Technical Compatibility Investigation

This article summarizes our technical investigation into the DPA 5 Code 39 driver error affecting certain DG Technologies adapters on modern versions of Microsoft Windows.

The findings below are based on real-world testing of multiple DPA 5 hardware revisions and are intended to help technicians diagnose driver compatibility issues.

Problem Description

Some legacy DPA 5 adapters fail to initialize under modern Windows systems with the following Device Manager error:

Code 39
Windows cannot load the device driver for this hardware.
System Integrity policy has been violated.

Windows Code Integrity logs may also report:

Code Integrity determined that NcBulk.sys did not meet the Microsoft Authenticode signing level requirements.

Hardware Comparison

During testing, two different DPA 5 hardware platforms were identified.

Legacy DPA 5	Newer DPA 5
USB VID_0525 & PID_A495	USB VID_0403 & PID_6B28
Uses NcBulk.sys	Uses FTDI driver (ftdibus.sys)
Driver dated 2010	Driver dated 2021
Fails with Code 39	Operates normally

Observed Behavior

The newer FTDI-based adapter was detected by Windows as:

DPA 5 Dual CAN USB Serial Converter
DPA 5 Dual CAN USB VCom Port

DG Technologies Adapter Validation Tool successfully established RP1210 communication and detected CAN traffic without errors.

The legacy adapter was identified as:

Dearborn Group DPA 5 (VID_0525&PID_A495) using NcBulk.sys

The legacy driver failed to load due to Windows Code Integrity restrictions.

Testing Performed

During troubleshooting the following configuration changes were tested:

Windows 10/11 Latest builds for 06.2026
Secure Boot disabled
Memory Integrity disabled
Test Signing Mode enabled
No Integrity Checks enabled
Removal of the latest Windows cumulative updates
Fresh installation of DPA Package 5.07

None of these changes allowed the legacy NcBulk.sys driver to load successfully.

Possible Root Cause

The investigation suggests that the problem is related to the legacy NcBulk.sys kernel driver rather than the adapter hardware itself.

The tested driver was originally released in 2010 and is digitally signed using an older Microsoft cross-signing certificate chain. Modern Windows Code Integrity policies may reject this class of kernel drivers even though their Authenticode signature remains technically valid.

This behavior is consistent with Microsoft's transition toward WHCP-certified kernel drivers and the gradual retirement of legacy cross-signed kernel drivers.

Recommendations

Verify the adapter Hardware ID before troubleshooting.
Identify whether the adapter is FTDI-based (VID_0403) or legacy (VID_0525).
If using a legacy adapter, verify whether DG Technologies provides an updated driver package for that specific hardware revision.
When purchasing used DPA 5 hardware, confirm the USB Hardware ID before deployment on modern Windows systems.

Current Status

At the time of writing, the FTDI-based DPA 5 hardware revision operated normally on Windows 10, 11 PRO while the legacy VID_0525&PID_A495 revision consistently failed to load the NcBulk.sys driver despite multiple compatibility tests.

Additional testing is ongoing to determine whether Windows Application Control (WDAC), updated driver packages, or alternative signing methods can restore compatibility for legacy hardware.