This warning displays if you attempt to paste an element to a location without a proper host.
Warning: Elements were deleted. Use Edit Pasted Elements to keep them.
Issue: Revit requires a proper host for the copied element. For example, a window needs a wall, and a tag or dimension needs reference elements.
Solution: If you tried to paste an element into a location that does not contain a proper host, you see this message. Click Cancel to remove the warning. On the ribbon, click Edit Pasted Elements. In Edit Pasted mode, place the copied element on its proper host. Click Finish to complete the paste process.