I got this error while trying to browse my SharePoint site from within the server. I tried in both my front ends and application server and got the same error. I double checked to make sure the user I'm trying to login to the site had enough permission and also that password had not expired or account locked. Nothing seems to help. Then I came across this excellent article by Spencer Harbar which talks about this issue. This error is caused by a feature in Windows Server 2003 SP1 and above called loopback security check. This feature prevents access to a site using its FQDN (Fully Qualified Domain Name) from the server that hosts the website. Here is Spencer's blog post: http://www.harbar.net/archive/2009/07/02/disableloopbackcheck-amp-sharepoint-what-every-admin-and-developer-should-know.aspx There is also a Microsoft KB article that gives a solution to this problem. There are two solutions, disable loop check through a registry entry (not recommended for production servers) ...
My experiences with SharePoint and other technologies