I found that my dlls must be each on different locations, for example interop.dll must be in bin folder, and gui.dll must be in Debug / Release folder where is validator.exe, after that validator run without problem. Problem arise when I want use my vst3 with those dlls outside Release folder. When they are next to vst3 file, it doesn help. And I have no clue where to add it. When I look at https://steinbergmedia.github.io/vst3_doc/vstinterfaces/vst3loc.html I tried create Resources folder and put dlls here, but it doesn’t help. Btw. plugin load with GUI when I use SAVIhost.exe where I build my vst3.