Digging up an old thread, but I faced this error last night setting up a development project on a fresh Install of Windows. I had VC++ Redist's installed as recommended (2015, 2017, 2019), also trying the one that came packaged in the security library, but it kept having same error: Unable to load DLL LIBSODIUM.DLL. Dataflex would also crash whenever I would add the library through "Manage Libraries"; giving same event error as OP.

I managed to fix it when I installed VC++ Redist 2008 & 2010. I'm not sure which one triggered the fix, but this is the only google result for such an error, so leaving this here if it helps anyone .