Problem loading add-in: The parameter is incorrect.

[Number8]

VisStudio 2008 add-in, created with the New Add-In Wizard, C#.

When I try to enable my add-in I get this:
The Add-in 'CBAddIn2' failed to load or caused an exception.
<snip text about renaming file...>
Error message: The parameter is incorrect.
Error number: 80070057


Here is the .Addin file:
<?xml version="1.0" encoding="UTF-16" standalone="no"?>
<Extensibility xmlns="http://schemas.microsoft.com/AutomationExtensibility">
<HostApplication>
<Name>Microsoft Visual Studio</Name>
<Version>9.0</Version>
</HostApplication>
<Addin>
<FriendlyName>CBAddIn2</FriendlyName>
<Description>CB Add-in</Description>
<Assembly
src="file">C:\Work\VisStudio_AddIn\CBAddIn2\CBAddIn2\bin\CBAddIn2.dll</Assembly>
<FullClassName>CBAddIn2.Connect</FullClassName>
<LoadBehavior>0</LoadBehavior>
<CommandPreload>0</CommandPreload>
<CommandLineSafe>0</CommandLineSafe>
</Addin>
</Extensibility>
What parameter is wrong, and how do I fix it?
Thanks.

[Number8]

Post by Number8
The Add-in 'CBAddIn2' failed to load or caused an exception.
<snip text about renaming file...>
Error message: The parameter is incorrect.
Error number: 80070057

The problem was in the OnConnect() method.
mainWindow =
(Window)_applicationObject.Windows.Item(EnvDTE.Constants.vsWindowKindMainWindow).Object;
threw a "Value does not fall within the expected range." exception, which
was displayed as "The parameter is incorrect".