Depending on your organization’s security policy and settings, the setup may be terminated with a security warning stating that the add-in’s certificate or its location is not trusted.
This may happen in particular when the setup is started from a network folder.
A possible workaround consists of temporarily copying the setup folder to a local folder (for instance to the Windows desktop) and starting the setup from there.
An alternative solution would be to add the add-in’s certificate to each client computer on which it is to be installed. The certificate can be found in the “setup.exe” file in the setup folder (right-click on “setup.exe”, then choose “Properties” from the context menu; in the “File Properties” dialog, look for the “Digital Signatures” tab, from where the certificate can be viewed and installed - either for the current user or the local machine). When asked to specify a location for the certificate, choose “Trusted Root Certification Authorities”.