For the installation to work properly the downloaded files need to be unzipped/extracted. Often individuals double click on the downloaded zip file; this opens up a folder to show what is in the zip file, but does not extract them. To avoid this problem go back to the original download file (EndNoteX(#) Installer.zip) and right click on it. This will bring up a list of options, choose Extract All... Once this is done go to the extracted files and double click on EXN(#)Inst.ms. This installation should now run and not ask for the product key.