Now that EPiServer SP1 is available, you might want to use the EPiServer CMS Manager to upgrade your site. Keeping that in mind, here is something nice to know.

When upgrading you might recieve this error message:

1. In the sites bin folder, check which version of EPiServer.Configuration.dll you are running.

2. Make sure web.config is referring to the correct version:

<configuration>
  <configSections>
    <section name="episerver" 
             type="EPiServer.Configuration.EPiServerSection, 
                  EPiServer.Configuration, 
                  Version=5.1.422.4, 
                  Culture=neutral, 
                  PublicKeyToken=8fe83dea738b45b7" />

3. Restart the EPiServer CMS Manager.

If you still receive the same error, make sure all the EPiServer files are installed in the GAC (and remember to restart your Manager).

PS: Make sure you are running EPiServer CMS Manager 2.0.19.3