dlls in SysWOW64 not found by application

Question

I'm developing a C#/WPF app that talks to a USB device using some custom 32 bit dlls. It's developed as an x86 app, and installed with WIX. When I install the package on a 64-bit machine, the program files get installed to Program Files (x86) as I expect.

The dlls are installed to the SystemFolder using WIX. On 32-bit machines, this means C:\Windows\System32. On 64-bit, they end up in C:\Windows\SysWOW64. This is ok, but when I run my app, it is unable to find the dlls (it uses them via [DllImport...]).

So, what is the right way to make my app find the dlls, whether they are in System32 or SysWOW64?

Thanks Tom

Answer 1

If it is a default C# app, it will automatically be a 64 bit app on 64 bit Windows (C3 defaults to 32 bit on 32 bit Windows). Go into the project properties in your development app and explicitly set the architecture (I think; I don't have Studio up right now) to 32 bit. If it is running as a 64 bit app, it won't be able to use your 32 bit DLLs.

Answer 2

Please check if the dll in application is of the same version as that in the sys32 or wow64 folder depending on your version of windows.

You can check that from the filesize of the dlls.

Eg: I faced this issue because my libeay.dll file in system32 had a different dll than my libeay.dll file in openssl application. I copied the one in sys32 into openssl and everything worked well.