I went to central admin via the host name (http://portal.company.com:75000) and went to "Site Actions > Site Permissions" then clicked on "Check Permissions" and a dialog box poped up to enter user/group name. I input user id and resolved it by clicking the man icon. Then clicked on "Check Now" and got an error "File Not Found".
I followed the exact same steps via this url http:/server:75000 and did not get the error.
How do I fix this?