The solution to this issue is very simple. I have based the details on Moggoly’s excellent Post
Firstly, you will need to show hidden files in what every version of Windows you using to host Visual Studio 2008. In the case of Windows 7 or Windows 2008R2: just click on the Organize button in any folder, and then select “Folder and Search Options” from the menu. Then go to the “View” tab and select “Show hidden files, folders, and drives”.
Next, you need to do is navigate to the one directories shown below depending which o/s you are using:
In either case you will need to delete the hidden files related to the toolbox: toolbox.tbd and toolboxIndex.tbd
Finally, restart VS 2008 and then breath a sigh of relief as all the missing “Windows Workflow 3.x” tabs are restored and with them the missing activities/items.
