windows blocks software because can't verify publisher

I'm trying to get set up to work as a remote agent. The communications software needs to load 3 programs (CCEmailClient.cab, WMencoderHF.cab, CCScreenRecorder.cab) and Windows gives this error message for each:

Internet Explorer Add-on Installer: Security Warning
Windows has blocked this software because it can't verify the publisher.
Name: [one of the 3]
Publisher: Unknown Publisher

I've downloaded .net framework 3.5sp1 without effect, though I'm not sure it's done what it's supposed to do.

I've played around with different changes to security settings and nothing has had effect. When I turn off the computer to disable Enhanced Protective Mode, it defaults to enabled when I turn the computer back on.

Any ideas how I might solve this problem?

Thank you, it did, along with setting custom security level to low.