Unable to load 'Refprp64.dll'.: The specified module could not be found.(Exception from HRESULT:0x8007007E

I am working on a thermal simulation program on Visual Basic 2010 Express, which requires a 3rd party REFPROP program link to estimate fluid properties.

I downloaded REFPROP wrapper from:

https://trc.nist.gov/refprop/LINKING/Linking.htm#NETApplications

(File name: ALKAN.ZIP)

Applied it to VB.NET and converted into dll file so that I can use it for my program.

The wrapper program also calls "Refprop.dll" file using "DLLimport" which I already have from REFPROP original source program from "NSIT" for Visual Basic.

In my thermal simulation program I can add a reference wrapper dll file but can't add the "Refprop.dll" file directly, and it shows the following error:

"Make sure the file is accessible and that is valid assembly or COM component".

However the wrapper DLL calls "Refpro.dll" using the DLLimport function, so I assume it will link Refprop.dll without adding it to reference directly.

But when I run my thermal simulation tool it calls wrapper DLL correctly, but doesn't link to "Refrop.DLL" and shows the error:

"Unable to load DLL'Refprop.dll': The specified module could not be found.(Exception from HRESULT:0x8007007E).

I tried to save the "Refrop.DLL" file in the "bin" folder as well, but it doesn't work.

I have a 64bit application, thus I tried to use "Refprp64.dll" as well, but I get the same issue. I appreciate your valuable comments on my issue.