Ok… this is what I blew my morning on and man that is not cool!  (scroll immediately to the bottom if you just want the easy fix!)

I created a new Webapp and Site Collection in a fresh Sharepoint Foundation 2010 server running Server 2008 R2 Standard 64 bit and found that I was being prompted for Username and Password Credentials even though I was logged in as Enterprise Admin.  After three apparently failed attempts at entering my existing (or any other admins) credentials, the prompt would go away and there was error visable.

I tried explicitly adding myself into the security via CENTRAL ADMIN – MANAGE WEB APPLICATIONS – [clicking on the WebApp in question] – USER POLICY (menu at the top of the window) – adding myself in.  No change.

I verified that the settings appeared to be the same on the default site as my site.

I tried extending the default site that the Sharepoing 2010 install created but I had the same problem.

I checked the Windows Server Security Event Log but found nothing interesting.

I Binged/ Googled the Hell out of this but found nothing useful.

I then blew my mind out and uninstalled – reinstalled Sharepoint Foudation 2010 from scratch.  Then I built a new Web Application and it associated Site Collection, but found I had the same damn problem… this was sure alot of fun!!!

I started checking other Windows Event logs and found this:

Log Name:      System                  Source:        LsaSrv
Date:          12/10/2010 1:49:45 PM
Event ID:      6037                          Task Category: None
Level:         Warning                        Keywords:      Classic
User:          N/A                                 Computer:      tanker-ms.ars1.local
Description:
The program w3wp.exe, with the assigned process ID 12668, could not authenticate locally by using the target name HTTP/billboard2.ars1.local. The target name used is not valid. A target name should refer to one of the local computer names, for example, the DNS host name.

Try a different target name.

Which after many tries in Google, I found the following via Bing which worked perfectly and solved the issue in about 30 seconds:

1. Go to REGEDIT > HKEY_LOCAL_MACHINE > SYSTEM > CurrentControlSet > Control > LsaMSV1_0
2. Right click MSV1_0 > New > Multi-String Value
3. Type ‘BackConnectionHostNames’
4. Right click & select ‘Modify’
5. Enter the Hostname of the site: WEBSITENAME (and on a new line enter the FQDN, WEBSITENAME.domain.com as well)
6. Restart IIS (be sure to RUNAS ADMINISTRATOR your IISRESET.EXE if you have UAC enabled)

And a big fat thank you to Terence of  http://www.dotnetpulse.com/?p=70

Also note that Up & Running is an MS Partner, so I posted this with the SPoint Team and was told that this KBase article explains the cause of this issue and that even though it refers to Windows 2003, it applies to all current versions, including Windows 2008 R2 Server 64Bit, which I am using.