Hello,
How do you have configured your veyon authetification methode, with keys or user auth?
If it's with keys it mean that users can't access to them, in configurator, view -> Advanced, Auth... keys, key file directories, add access to the group users.

@jesse26j I downloaded it from the veyon website, not from github. It says version 4.7.4.0 in Windows.

Grey screen usualy mean that computers do not communicate, if you use LDAP does the "integration test" work well? If you use "locations & computers", do you enter IP or machine name? If you use machine name can you ping the client with his name from the Master?
You may have firewall on PC or access lists in switchs that can block TCP ports?

@darrellsimone The documentation should be read first: https://docs.veyon.io/en/latest/admin/installation.html#installation-on-a-linux-computer

The teacher machine needs veyon configurator, the client machines only need veyon master.

In principle, you can also access a machine on an external network, although I haven't tried it yet, but you have to enable Veyon on the firewall. If something doesn't work, feel free to ask, I'm happy to help if I can.

@bacsom you welcome! I think you already checked the windows firewall, trying to disable it on both Student and Teacher Pcs. The next step I would check from Lan "Network properties" would be to see if both student and teacher PCs are on "Private" (not Public) network . If all of these settings have been checked maybe some traffic is blocked by the school's router/firewall? Have you even been able to use Veyon's Demo in older releases?

@Luigi-Capp I have fixed it with the command "sudo apt-get -f install /home/luigicapp/Scaricati/Temp/veyon_4.7.5.0-ubuntu.jammy_amd64.deb"
Luigi Cappellazzo

Are you using the latest version on both teacher and student computers?

A typical mistake is that Veyon add-ons are not installed on student computers. Also make sure to configure the Internet access blocking mechanism client-side. Is the Windows Firewall enabled on student computers? If not, please enable it and don't set any group policy which prevents applications from changing the firewall configuration.

This can be easily done with PSTools from Microsoft and a batch script or PowerShell.
I use the following to manually remotely install veyon and the security keys when the GPO installer doesn't work for any reason.
You can replace line 1 with a call to a list of computers rather than specifying a single computer if that fits your needs better.

SET /p computer="enter computername:" XCOPY "\\networklocation\veyon-4.7.5.0-win64-setup.exe" "\\%computer%\C$\" /e /h /y XCOPY "\\networklocation\UserConfig.json" "\\%computer%\C$\" /e /h /y XCOPY "\\networklocation\veyon\Veyon\*.*" "\\%computer%\C$\ProgramData\Veyon\" /e /h /y timeout /t 5 CD "C:\PSTools\" psexec64 \\%computer% C:\veyon-4.7.5.0-win64-setup.exe /S /ApplyConfig=C:\UserConfig.json /NoMaster

Hi,
after the reboot command when all my calssroom PCs shows the desktop if I hit "F5" then I can get back them all visible in veyon master.
This is only a small issue but wasn't present in 4.7.4 release.
Have a good day.