Why can I only login if I use “Sign in as a different user”?

Question

Currently, I can only login directly (in any browser) with members of the Sharepoint Farm Administrators group. However, if I login as one of those administrators then login as a regular domain user I am able to login just fine.

For example:

Company / Domain: "MyCompany" Regular Domain user login: "UserA" (also a member of AD group "MyCompany\Company Employees") -Yes there is actually a space in the name of the group Domain Admin / Sharepoint Farm Admin / Site Collection Login: "DomainAdminA"

I CAN login as "MyCompany\DomainAdminA" and THEN "Sign in as different user" with "MyCompany\UserA"

I CAN NOT login directly as "MyCompany\UserA".

One thing to note, this is a new installation. I have upgraded 5 site collections from 2007 to 2010 and imported them into the same Web Application - and when I log into those site collections (ie. https://intranet.company.com/sites/collection1" I AM able to login directly. But when I try to log in directly to https://intranet.company.com I am NOT able to login as UserA - only as DomainAdminA then Sign as Different User with UserA.

Answer 1

I didn't want to take credit for answering my own question so i did it as an edit but the following resolved MY issue:

UPDATE: The issue had to do with the fact that the Security Token Service was not functioning properly. I'm still not sure that i'm clear on how to correctly change managed service accounts, passwords, etc. But I DID get it working. I guess I was able to login with the Domain Admin account because that account is a Farm Admin (so I guess somehow it did not need to utilize the Security Token Service). And once I was logged in, i'm guessing there is some sort of authentication caching going on that allowed me to switch to a user account that was not directly specified within Sharepoint (Company\UserA)? Whereas trying to initially login with Company\UserA did require the Token Service to be functioning properly? I have no idea but I did get it working. If anyone wants to take a stab as to what they guess was happening i'd love to hear it. Thanks again Rob.