Cany install WPMUDEV on http://irishlakelands.com

Hi, I have successfully installed WPMUDEV on several other of my sites. But when I attempt to log in after uploading and activating the plugin on http://irishlakelands.com I get the following error screen message.
code "rest_missing_callback_param"
message "Missing parameter(s): username, password, redirect_url"
data
status 400
params
0 "username"
1 "password"
2 "redirect_url"