Another option is to use the Copy in the Data Management geoprocessing tool to make a copy of the input data.
* If a feature class is copied to a feature dataset, the spatial reference of the feature class and the feature dataset must match; otherwise, the tool will fail. * The Copy tool does not support copying a network dataset back into the same geodatabase. If that fails, a reboot of the program could free the virtual memory that might cause the copy/past special process to fail.
May I ask, are you attempting to copy features using editing tools from one feature class to another? Can you check that the destination feature class is check marked to allow editing and is visible?
