Please have a look here:
Process Interoperability - Win32 apps | Microsoft Docs[
^]
There it is said:
On 64-bit Windows, a 64-bit process cannot load a 32-bit dynamic-link library (DLL). Additionally, a 32-bit process cannot load a 64-bit DLL.
Switch your application to 64bit and get 64bit versions of the third party dlls
or stay at 32 bit and create a 32 bit library project.