I came across this today. Just a heads up.
1) Installed BES 10.
2) Was able to log in SUCCESSFULLY right after installation of BES 10 via https://[YOUR SERVER NAME
3) After about two hours, the EXACT SAME credentials failed to work. It would come up and say my User ID, Password or Domain failed (in red text).
This appears to be a minor bug with BES 10 (as documented on the BlackBerry support site).
All you need to do is do an ipconfig /flushdns on the BES 10 server.
This corrected the problem and the same credentials will start working again.
Just a heads up. It was not instantly evident when I Googled it at first, but I found it after about 45 minutes of searching.