SetSite failed for package [Visual Studio Class Designer Package]

When starting Visual Studio you get a pop up which contains the following error:
The package 'Visual Studio Class Designer package' has failed to load properly. GUID {DD1683A7-5A4C-4234-81B3-A4CC91DBEAC9}
Close Visual Studio.

Now start Visual Studio with devenv /log

Navigate to the log location, normally:
C:\Users\username\AppData\Roaming\Microsoft\VisualStudio\10.0\ActivityLog.xml
If this log contains the following entries:

<entry>
 <record>208</record>
 <time>2012/01/17 15:06:00.310</time>
 <type>Information</type>
 <source>VisualStudio</source>
 <description>Begin package load [Visual Studio Class Designer Package]</description>
 <guid>{DD1683A7-5A4C-4234-81B3-A4CC91DBEAC9}</guid>
</entry>
<entry>
 <record>209</record>
 <time>2012/01/17 15:06:00.412</time>
 <type>Error</type>
 <source>VisualStudio</source>
 <description>SetSite failed for package [Visual Studio Class Designer Package]</description>
 <guid>{DD1683A7-5A4C-4234-81B3-A4CC91DBEAC9}</guid>
 <hr>8000ffff - E_UNEXPECTED</hr>
 <errorinfo>Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED))</errorinfo>
</entry>
<entry>
 <record>210</record>
 <time>2012/01/17 15:06:00.415</time>
 <type>Error</type>
 <source>VisualStudio</source>
 <description>End package load [Visual Studio Class Designer Package]</description>
 <guid>{DD1683A7-5A4C-4234-81B3-A4CC91DBEAC9}</guid>
 <hr>8000ffff - E_UNEXPECTED</hr>
 <errorinfo>Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED))</errorinfo>
</entry>

Now start Visual Studio with devenv /ResetSettings

If this doesn't work, then repair or re-install Visual Studio.