I cannot install plugin on WPMU Dev

Hi Support Team

First time I try demo install all plugin on WPMU Dev in my domain saratit.com (test domain site)

and now i want to set up all plugin with the domain sernero.com but i cannot install on WPMU DEV

Message Error
"An unexpected error occurred. Something may be wrong with WordPress.org or this server’s configuration. If you continue to have problems, please try the support forums."

Help me please