Mitch Wheat - Treat the cause, not the symptoms!

Update: although this works, it makes VS2010 open really slowly...

There does not seem to be an installer for VS2010. You can install the VS2008 version of CopySourceAsHtml (from here), and then manually edit the CopySourceAsHtml.AddIn file located at C:\Users\<username>\Documents\Visual Studio 2010\Addins so that both Version elements are set to 10.0:

<?xml version="1.0" encoding="utf-8" standalone="no"?>

<Extensibility xmlns="http://schemas.microsoft.com/AutomationExtensibility">

<HostApplication>

<Name>Microsoft Visual Studio Macros</Name>

<Version>10.0</Version>

</HostApplication>

<HostApplication>

<Name>Microsoft Visual Studio</Name>

<Version>10.0</Version>

</HostApplication>

<Addin>

<FriendlyName>CopySourceAsHtml</FriendlyName>

<Description>Adds support to Microsoft Visual Studio 2008 for copying source code, syntax highlighting, and line numbers as HTML.</Description>

<Assembly>JTLeigh.Tools.Development.CopySourceAsHtml, Version=3.0.3215.1, Culture=neutral, PublicKeyToken=bb2a58bdc03d2e14, processorArchitecture=MSIL</Assembly>

<FullClassName>JTLeigh.Tools.Development.CopySourceAsHtml.Connect</FullClassName>

<LoadBehavior>1</LoadBehavior>

<CommandPreload>0</CommandPreload>

<CommandLineSafe>0</CommandLineSafe>

</Addin>

</Extensibility>