That's just the standard welcome message, not an error message. Error messages will be in red, not yellow.
If you can provide an error message, we may be able to assist, but for the time being, there's nothing to assist with.
Probably the most common cause for not being able to run a command that I tend to see is the person does not have the necessary rights granted to them within Exchange to run the command. But again, this is just a general tip since your screenshot has nothing specific to focus on.