Group email recepient does not receive the email

I am running into a problem, that I have a address group that all of the recepients receive the email, but one. All of the recepients are internal, but I can not figure this one out? Has anyone experienced this and have a fix for it?

Thanks

Subject: Group email recepient does not receive the email

Was the problem user’s name added to the group by using the address picker, or was it typed in? Is there a typo in the name? Is the full hierarchical name used, or just the common name?

Subject: RE: Group email recepient does not receive the email

It was added in with the address picker. No typo (that was the first thing I checked)