WPMU Dashboard Plugin won't install

Hi
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.
Try:
Checking the connection
Checking the proxy and the firewall
ERR_CONNECTION_RESET

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,
Vanessa