Hi Juergen,
Are those other agents also assigned to the Service Desk Team role of the Service desk project where you are trying to assign them?
If that's not the case, that could be the answer to your problem. If they are, have a look at the permission scheme of your Service Desk project. The Service Desk Team role should be granted the assignable user permission.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.