WPMU Dashboard Plugin won't install

I am trying to install the WPMU Dashboard plugin on the site http://www.acebiology.co.za/learners-area so that I can install the Ultimate Branding plugin so that I can fix the way the login screen looks to users, but whenever I upload the zip file, I get a message that says:
This site can’t be reached

The connection was reset.
Checking the connection
Checking the proxy and the firewall

The site is hosted with Heart Internet. Could that be the problem?

I'd appreciate any help you can offer. It's very urgent.

Many thanks,