The following quote ocured:
Your server had a problem connecting to WPMU DEV. Please try again.
If this problem continues, please contact your host and ask:
"Is php on my server properly configured to be able to contact https://premium.wpmudev.org/wdp-un.php with a GET HTTP request via fsockopen or CURL?"
Unfortunatly my server provider has no idea hat this meant, when I contacted their technical support.