Script not working from one computer

I know, PHP is executed server side, so it shouldn't matter about the computer, but... I've got a basic log in script that takes username and password and does the typical SELECT to find a match. If it's good, it sets some session variables and redirects to a main page, otherwise redirects back to the login page with an error message. The script works from all computers but one. The login page will come up, but no matter what, it says the username and password are bad. They are correct though, caps lock isn't on, etc. I've cleared the cookies and cache and it still does the same thing. The script is on an intranet. One computer that had this issue was fixed by using https://computername.company.army.mil instead of just https://computername. But for this computer, both addresses give the same result. So, I'm sure it's not the PHP script, so I'm looking for ideas of what I should check, settings wise, on the client computer? Any help is greatly appreciated. ---John Holmes...