Autodesk's Civil3D and Land Desktop create custom entities called AEC Objects instead of standard AutoCAD entities. When Civil3D or Land Desktop is not available on a computer that is opening a DWG file which these objects, those objects become "stranded" and are commonly referred to as "proxy" objects.

Drawings which contain AEC Objects cannot be used with SurvCE or SurvPC.

Carlson has two routines to convert these objects:

1) is within Drawing Cleanup and works on AEC Objects within the drawing and 
2) under Surface (or Tools) > Import/Export > Convert LDT/Civil3D Surface Drawing which creates a new drawing with the AEC Objects converted.

A third tool to be aware of is Autodesk's free DWG TrueView available for download here:

http://usa.autodesk.com/adsk/servlet/pc/index?id=6703438&siteID=123112

After opening up the program, click on the  Convert  icon from the pull-down menu. From here select the drawing(s) to convert and then the "Conversion Setups" button then "Modify".

From the "Modify Conversion Setup" dialog select a Drawing Format that includes "With Exploded AEC Objects." If you are using an older version of AutoCAD, you can also select back to AutoCAD 2000. 

Select OK and you are done.