You might want to try a simpler example first: (rdnzl:load-assembly "System.Windows.Forms") --- this should give something like #<RDNZL::CONTAINER System.Reflection.Assembly #x9D70E8> If that doesn't work, you should try (ccl:open-shared-library "RDNZL.DLL") If that works, you need to look at rdnzl:invoke, and the functions called by rdnzl invoke.