Building Office 2007 add-in failed due to missing dll's

I had worked some time on a Word 2007 add-in in Visual Studio 2008. After a while, it did not work anymore. I got the following error:

Error   1   The "VerifyClickOnceSigningSettings" task could not be instantiated from the assembly
"Microsoft.VisualStudio.Tools.Applications.BuildTasks, Version=9.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a". System.TypeInitializationException: The type initializer for
'Microsoft.VisualStudio.Tools.Applications.Hosting.CodeGeneration.VerifyClickOnceSigningSettings'
threw an exception. ---> System.IO.FileNotFoundException:
Could not load file or assembly 'Microsoft.VisualStudio.Tools.Applications.Hosting.v9.0,
Version=9.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'
or one of its dependencies. The system cannot find the file specified. File name: 'Microsoft.VisualStudio.Tools.Applications.Hosting.v9.0, Version=9.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' at Microsoft.VisualStudio.Tools.Applications.Hosting.CodeGeneration.VerifyClickOnceSigningSettings..cctor()

Unfortunately, there was almost no documentation on this error. I tried a 'correction' setup and also run the SP1, but that didn't work out. Finally, I found it on http://www.tech-archive.net/. You need to download the Microsoft Visual Studio Tools for the Microsoft Office system (version 3.0 Runtime) (x86) (download here). Run this setup and this will fix the problems.

Don't ask me why it worked before and later on not anymore, I don't know. MS stupidities perhaps? ;)