Installation: Certificate is not trusted

Try to install the latest version from our website by this link: https://www.ahausoftware.com/redmine-outlook/download

Try install with an option for All Users of this Machine.

Note: Make sure you unselected and selected that option manually. It can be selected by default.

Enable the checkbox Accept the terms in the License Agreement:

Please check that you have installed the last windows updates and check the signature of the installation file.

Windows Products KB