(Offline installation) When installing SharePoint Essentials Toolkit I get an error: disk1.cab has an invalid signature. The download file seems fine, what's wrong?!

The application uses Code Signed Digital Certificates to valid its authenticity and to ensure it is a Trusted Application.

The error can occur for a number of reasons, the most common is not having internet access.

The core of the problem is that your Windows installation is unable to contact the certificate provider that can verify the installer’s security certificate.

Workaround

Download and install the certificates here, then install by right clicking on the downloaded files, one at a time. Choose automatic to determine the target location to install to.

Instructions

1.       Copy the certificates to the computer where the tool will be installed
2.       Right click and click Install Certificate
3.       Choose Local Machine
4.       Click Next
5.       Choose ‘Automatically select the certificate store based on the type of certificate’
6.       Click Next
7.       Click Finish
8.       Repeat above for both certificates