We are aware of this and it’s because the main website has been upgraded and now has a stricter HTTPS policy, which means that once you’ve visited that site your browser will require a HTTPS connection for all sub-domains.
Just to be clear, downloads.myriadrf.org does not have a server certificate and is presently HTTP only. The error message is confusing…
We do plan to move downloads.myriadrf.org over to SSL, but first we need to validate that LimeSuiteGUI and LimeUtil will still be able to download updates. In the meantime you can just open a “private” browser window.