Yesterday a user had the problem that a canceled meeting could not be removed from a meeting workspace. After searching the Internet I found the following article on the Microsoft site: Removing a Meeting from a Meeting Workspace
It is not possible to solve this issue via the GUI, but you have to do this programmatically via the Sharepoint object model. This article describes the steps to be taken and provides a small piece of example code. Just follow the steps in the article (make new C# project and past the code) and run the program. Then enter the meeting workspace url and id of the meeting which should be canceled.....and voila now you can delete the meeting via the GUI.