Autocad 2010 files are not backward compatible with 09-. What you would have to do is to wblock out, save the block to 2007 then import that. You can't use the clipboard to back down. Takes more steps, but it's doable.
Also, if you go to C3d, the civil objects won't transfer. You'll have to xml them out and import them into LDC w/ xml.
Reid