Install you DLL assembly by using the ‘gacutil.exe’, before installing the DLL ensure it has a strong name, to assign a strong name refer to the link Assigning a DLL strong name .
1) open the Command prompt, and navigate to the folder of gacutil.
2) To install a DLL assembly
gacutil /I "C:\[PathToBinDirectoryInVSProject]\gac.dll"
3) To uninstall
gacutil /U “Name_of_The_DLL”