Share for "Domain Users" works for admins but not for other users


I’m evaluating UCS at the moment and installed it as domain member in an existing Microsoft AD Domain. Everything worked fine so far. I can manage the server with UMC from my admin account and not from my user account.

Now to my problem:
I’ve created a simple share with root as owner and owner group “Domain Users” as all Users of our AD are members there. However, in Windows Explorer I can access the share with my Admin-Account via DNS-Name and IP-Address.
When I try to access the share via IP with my normal user in Windows, a message pops up that there is no access possible and I have to check network settings. When I try to access the share via DNS (\DNS-Name) I get a login-window where the credentials of my normal user are not guilty - but it’s working with my admin-credentials.

I don’t know if this problem is maybe AD-related (maybe GPO-problem) as I’m not managing the AD stuff in our house.

Maybe someone has an idea. Thank you for your help in advance.