Hi David,
I believe I've seen this happen in the past when the stored procedures aren't updated properly. Here's a quick way to see if the stored procedures are retrieving the right data. Find out what your portal id is. If it's the default portal, then your portal id is 0. You can check this in Host | Portals. Next go to Host | SQL and execute the following SQL:
EXEC {databaseOwner}{objectQualifier}Blog_GetEntry 72,0
Where 72 is the EntryId of the latest post I found on your site and 0 would be the portal Id you looked up above. You should see data returned from this query. If not, then you may want to check your web.config file to make sure that the connections strings are pointed to the right version of the database. I've had issues before where my web.config was pointing to a backup version and not the upgraded version.
Of course, before you do anything that would update the database, like the steps I recommend next, please backup your database and your DotNetNuke folder to ensure that you don't lose data in the process!
If this doesn't work then you may want to manually execute the SQL found in the SqlDataProvider files starting with 03.01.04.SqlDataProvider. You can execute these using the same Host | SQL tool referenced above. Also, make sure to execute these files sequentially starting with the earlier versions first.
If you recieve error messages while executing these files, then copy these messages into Notepad or some editor and then you can include them in a post back here on the forum to see if others can help figure out what might be the problem.
HTH,
Don