What I have found is to many programs are using the SQL Express server and as a result I get an error that I'm limited to 8 transaction or something like that.  I have SQL 2005 Standard on the server, and when I loaded DNN it loaded it's own.  I transfered the DNN database from Express to standard, and everything on that side looks good.  However when I then updage the webconfig file to point to the standard database instead of express I get the following error.

DotNetNuke Upgrade Error

The Assembly Version ( [ASSEMBLYVERSION] ) does not match the Database Version ( [DATABASEVERSION] )

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: 26 - Error Locating Server/Instance Specified)

I have check for remote access issues and it all looks good.  The username and passwords should all be the same from the old database as I did a full transfer (if this isn't the case, that's prob where the issue is).  All the accounts that were in the old database were transfered to the new one.  Any ideas?  I've been battling with this one for a few days now.

I figured it out:

I bet you changed the name of the Add key value
It NEEDS TO BE SiteSqlServer

<add key="SiteSqlServer" value="Server=webserver;Database=Website;uid=;pwd=;"/>

I had made it the name of my sql server:  Once I changed it back to SiteSqlServer all was fine.