Sharepoint error message - "Sorry, you don't have access to this page"

Hello,

Not sure if this is a SharePoint issue or IIS, but here goes:

When we browse to a site called test.test.edu, we get the message "Sorry, you don't have access to this page"

However, we browse on level deeper - test.test.edu/test, the site works.

Please help if you can!

Craig