@Chanwoong_Jang is that possible to post the error message or screen shot along with the studio version you are using , Global Assembly Cache (GAC) is the centre place to refer common library packages, before deleting it make sure it is not referred by any other application for eg visual studio.
Sorry for resurrecting this old thread. Hi @Chanwoong_Jang were you able to solve your problem? I have another customer experience the same issues with Newtonsoft.json.dll because it is used by both UiPath Studio and their internal application.