I/O Error when loading an ExternalObject (dll) in Extendscript

I've been experimenting with the ExternalObject feature because I want to integrate a c++ library with my After Effects script. I started with the SampleLib found in the path:

C:\Program Files (x86)\Adobe\Adobe ExtendScript Toolkit CC\SDK\Samples\cpp\build\samplelib

I used VS 2019 to build the solution and got a dll file out of that. Then when I try to load it with:

var lib = new ExternalObject("lib:SampleLib.dll");

 What I get is:

I/O error

I'm not sure what to do at this point. The documentation does not even mention this as a possible error. I've looked everywhere on the internet but I can't seem to find anyone with a similar issue. It seems to work fine for everyone.

Any help would be appreciated!