Just to make sure, check with network admin that your MAC address is not blocked :)
The message posted indicates you might have a Firewall setting issue.
Open About this Mac + more info + system report and find the Firewall. Check the settings there making sure it is not blocking that network somehow.
Also make sure you do not have a 3D party Network software blocking that connection like Little Snitch or others.
Lets try to connect manually, using the Terminal:
Follow this guide to connect using copy paste.
In Terminal type following (to turn the airport on)
networksetup -setairportpower en0 on
Next type (to scan for networks and find the one you want)
/System/Library/PrivateFrameworks/Apple80211.framework/Versions/A/Resources/airport scan
Finally type (to connect)
networksetup -setairportnetwork en0 WIFI_SSID_I_WANT_TO_JOIN WIFI_PASSWORD
If the password is something weird like ASCI or HEX follow this guide.
Look up your model here.
http://www.everymac.com/systems/apple/mac_mini/index-macmini.html
Then, scroll down to the section marked "Maximum MacOS:", it's towards the bottom on the right.
One of my Mac Minis is the early 2009 Core2Duo model, which is the oldest Mini which supports Yosemite. If you have a model which is older than 2009, it will only support Lion (Core2Duo), Snow Leopard (CoreDuo/CoreSolo), or Leopard (PowerPC).
Best Answer
Click Anywhere, then Apple -> Select Startup Disk -> Restart.
This is the same as this question. High Sierra - The path /System/Installation/Packages/OSInstall.mpkg appears to be missing or damaged