I don't think you actually need to add the certificate in the connection settings. I'm in a similar setup at work. I added it, like you, through the file manager, as wifi certificate, and it seems to be picked up automatically, even when choosing None in the settings (prior to adding the certificate, I could connect as well, but getting a Certificate warning message).

I think your issue might be in how you entered the username. Make sure it is of the form username@domain . You also need to add it a 2nd time in the Advanced/EAP Settings screen, under Manual Username (and check the Use Manual Username checkbox).