Had a whole host of errors while working with a new Sharepoint Server installation. I’m using Sharepoint 2010. I couldn’t add document libraries to subsites. I couldn’t update information in a datasheet view of a custom list. I would get “site could not be found” errors on setting up document libraries. I would get “page could not be found” on the datasheet problem. I had actually found the solution about 10 minutes into researching the first problem. I continued to spin my wheels looking for other solutions because I had applied the first solution incorrectly. Part of my problem was that my installation of MS Office 2007 was not quite right. The MS Office diagnostic tool found a problem and corrected it. That changed the second error into an error about a response returning from a different domain from where Internet Explorer sent the request. That was while updating the datasheet view. Aha!
The fix was by going to the Alternate Access Mappings in the Central Administration tool and adding the FQDN of the server under the base site name on port 80. Both problems went away when I did that.