Hi Phill,
To read the logfile, download the \data\currentlog.config file using FTP and open it with a text editor.
The error makes me think that you kept your old web.config file or not all of the files got uploaded when you upgraded. If you did keep your old web.config, you need to use the web.config from the release files. If you didn't keep your old web.config, you should try uploaded all of the files from the release again.
Thanks,
Joe D.