OK, I just tried to replicate your problem and was able to do so. Make absolutely sure that you have glfw3.lib OR glfw3dll.lib added to "project properties->Linker->Input->Additional Dependencies" for EVERY configuration. I think that you added the library for either your Release or Debug configuration, but not both. I've done this more than once. I found it helpful to get into the habit of changing the project configuration to "All Configurations" before setting directories and adding libraries. Saves a LOT of headaches!