"Not found" exception on loading referenced .NET DLL that is in same folder as referncing .NET DLL


I have a .NET DLL SigToolNet.DLL with multiple visible COM classes. It references a .NET DLL FTDIVcpLibNet.DLL wrapper for a native C++ static library FTDIVCPLIB which in turn references 3rd party native DLL ftd2xx.dll. The SigToolNet.DLL is registered with the 32 bit regasm successfully

C:\Release> regasm SigToolNet.dll /codebase
RegAsm : warning RA0000 : Registering an unsigned assembly with /codebase can cause your assembly to interfere with other applications that may be installed on the same computer. The /codebase switch is intended to be used only with signed assemblies. Please give your assembly a strong name and re-register it.
Types registered successfully

Side note, I don't know why it's giving me this warning since SigToolNet.dll is code signed. When running on the development system where VS2019 is installed the application TestHarness.exe which references COM visible class in SigToolNet.DLL runs successfully. However, when SigToolNet.DLL is installed on another computer I get an exception at run time at the point where the 2nd call to one of the COM visible methods (DetectDevice) is called

Command DetectDevice failed
Error code: -2147024770
Desc: Could not load file or assembly 'FTDIVcpLibNet.dll' or one of its dependencies. The specified module could not be found.

All referenced DLLs including FTDIVcpLibNet.dll are located in the same folder where SigToolNet.DLL is located which is also where it was registered.

I've tried running on 3 different computers all with the same failed results on both Windows 7 and Windows 10. The development system where it runs successfully is running Windows 10.

I also tried tracing the assembly load failure with Assembly Binding Log Viewer (fuslogvw.exe)

*** Assembly Binder Log Entry  (6/26/2020 @ 4:00:00 PM) ***

The operation failed.
Bind result: hr = 0x80070002. The system cannot find the file specified.

Assembly manager loaded from:  C:\Windows\Microsoft.NET\Framework\v4.0.30319\clr.dll
Running under executable  C:\Vendor Testing Harness\Epic 2018 And Beyond\EpicESigTestHarness.exe
--- A detailed error log follows. 

=== Pre-bind state information ===
LOG: DisplayName = SigToolNet, Version=2020.0.0.3, Culture=neutral, PublicKeyToken=null
LOG: Appbase = file:///C:/Vendor Testing Harness/Epic 2018 And Beyond/
LOG: Initial PrivatePath = NULL
LOG: Dynamic Base = NULL
LOG: Cache Base = NULL
LOG: AppName = EpicESigTestHarness.exe
Calling assembly : (Unknown).
LOG: This bind starts in the default load context.
LOG: Download of the application configuration file was attempted from file:///C:/Vendor Testing Harness/Epic 2018 And Beyond/EpicESigTestHarness.exe.config.
LOG: Configuration file C:\Vendor Testing Harness\Epic 2018 And Beyond\EpicESigTestHarness.exe.config does not exist.
LOG: No application configuration file found.
LOG: Using host configuration file: 
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v4.0.30319\config\machine.config.
LOG: Policy not being applied to reference at this time (private, custom, partial, or location-based assembly bind).
LOG: Attempting download of new URL file:///C:/Vendor Testing Harness/Epic 2018 And Beyond/SigToolNet.DLL.
LOG: Attempting download of new URL file:///C:/Vendor Testing Harness/Epic 2018 And Beyond/SigToolNet/SigToolNet.DLL.
LOG: Attempting download of new URL file:///C:/Vendor Testing Harness/Epic 2018 And Beyond/SigToolNet.EXE.
LOG: Attempting download of new URL file:///C:/Vendor Testing Harness/Epic 2018 And Beyond/SigToolNet/SigToolNet.EXE.
LOG: All probing URLs attempted and failed.

I find this log confusing. It says it fails to locate SigToolNet.dll but it appears to be looking for it in the same folder as the TestHarness.exe. It should be looking for it in C:\Release which is where SigToolNet.dll was successfully registered. Also, the reported exception is not that it couldn't find SigToolNet.dll but that it couldn't find FTDIVcpLibNet.dll. Shouldn't the first place it looks be the same folder where SigToolNet.dll is registered?

I've used remote debugging in VS2019 and have been able to breakpoint and single step in SigToolNet at the call to the first method Init. But the breakpoint on the 2nd call to DetectDevice never happens due to the exception before the call executes.

All .NET DLLs are using .NET 4.8

I have been unable to determine why it runs successfully on the system where SigToolNet.dll was developed and VS2019 is installed but not on other systems.

asked on Stack Overflow Jun 27, 2020 by JonN • edited Jun 27, 2020 by JonN

1 Answer


Possible you have to install approciate version of C++ Redistribatable for your FTDIVCPLIB.dll. On machine with VS2019 your have already had it.

answered on Stack Overflow Jun 27, 2020 by Lana

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