If, when you attempt to install EndNote (having downloaded and unzipped/extracted the installation file correctly), your computer tells you that the file is invalid or corrupted, the security or firewall settings on your computer might be preventing the successful creation and/or extraction of compressed files. Review these settings, then try to download, extract and install the EndNote file again.
If you are using a PC or laptop supplied/maintained by Queen's and experience this problem, you should contact your local (i.e. school, centre or department) IT team and ask them to review your device's security/firewall settings. Alternatively, contact the main IT Help Desk: https://www.qub.ac.uk/directorates/InformationServices/Services/ITServiceDesk/