I hope this helps others with the same error I had.

I have had our DotNetNuke site up for 2 years now with no problems.
 
http://www.acocares.org/aco/
 
No changes have been made to the files on the site (other the jpg's and pdf's).  No changes were made to the webpages for 3 days before the error.  This is a very simple site with a very simple DNN DB that has not changed in years.  As of Friday August 16th, the site has been down with the following error:
 

ERROR: Could not connect to database.
 
An error has occurred while establishing a connection to the server. When connecting to SQL Server 2005, this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections. (provider: SQL Network Interfaces, error: 0 - Insufficient system resources exist to complete the requested service.)

After hours of emailing the hosting company and checking DB connection strings and verifying that the SQL DB was just fine I found this:

Here was the fix:
www.fasthostinghelp.com/error-assembly-version-assemblyversion-t81.html?s=baa9a3b38c595dcfbc00f837d7e5d687&s=fecd12ee7902be831c6bf9ebcf5971ca&p=160

Even though the site had never been upgraded or the config (or any) files modified since it was setup 2 years ago, the "web.config" file still needed to be updated to make the site work now.

Here is the entry that needed to be made in the web.config under appSettings:

add key="UseDnnConfig" value="false"

I hope this information will help others, though I am still very baffled by what made this setting necessary after all this time.

Does anyone have an idea why this change was needed after all these months of flawless uptime?