Blender Version
Broken: 2.69

Short description of error
Copy-button and operator on command line work, but it shouldn't appear in the spacebar menu, since it will always raise an error:

The object the data pointer refers to is not a valid modifier

http://blender.stackexchange.com/questions/6960/how-do-i-successfully-copy-modifiers

Exact steps for others to reproduce the error
Hit Spacebar over 3D View and run Copy Modifier operator