To Add a dll reference to a project from GAC, you can’t use normal way to navigate to C:\Windows\assembly folder to select the dlls.
The actual path to the dlls in the GAC are C:\Windows\assembly\gac_msil\\_\.dll, however, before you can navigate to this path, you need run the following to make it visible to you.
type : “cd\windows\assembly”
type: “attrib -r -h -s desktop.ini”
type: “ren desktop.ini desktop.bak”
now you can open it and add reference.
To revert back to the original structure, run
Ren desktop.bak desktop.ini
It will revert back to original view