The keyboard short-cuts for Copy (Ctrl+C) and Paste (Ctrl+V) may not work if the "Editor/debugger key bindings" preference is set to "Emacs" instead of "Windows".
In order to check the MATLAB Keyboard preferences n MATLAB 7.8 (R2009a) go to File -- > Preferences --> Keyboard and look for the "Editor/debugger key bindings" options on the "Keyboard Preferences" pane. If the "Editor/debugger key bindings" option is set to "Emacs", the Copy (Ctrl+C) and Paste (Ctrl+V) features will be disabled. To enable these features, change the "Editor/debugger key bindings" option to "Windows" and click on the "Apply" button in the right bottom corner of the "Preferences" window.
If you are using MATLAB 7.9 (R2009b) - MATLAB 7.14 (R2012a) go to File -> Preferences -> Keyboard -> Shortcuts, or for MATLAB 8.0 (R2012b) - MATLAB 8.2 (R2013b) click the Preferences button in the Environment section of the Home tab and navigate to Keyboard -> Shortcuts. Make sure that under Active Settings, "Windows Default Set" is selected. This will ensure that the Keyboard Shortcuts Preferences are mapped to the default Windows settings i.e. Copy (Ctrl+C) and Paste (Ctrl+V).
Note: Make sure that there are no conflicts listed under the 'All Possible Conflicts' section if you included other customization.