Roundcube only works for email domains hosted for customers. It generally doesn't work for @riverland.net.au addresses, unless they have a special arrangement. For @riverland.net.au addresses, use the usual Telaen webmail.
If your address is definitely on this server - check you've entered your whole email address - this one expects the bit after @ as well - and type the password carefully.
Roundcube requires a fairly new browser. It requires javascript ON. If you have an older browser, try squirrelmail instead. It can work without javascript.
Try double clicking the message. Alternatively, click the up-triangle at bottom right and a “preview” pane will open at the bottom of the message list. You can make this permanent in the Preferences.