I'm using Land Desktop Companion with Civil 3d 2009, Windows XPsp3, sometimes if you type aecopen at the command line, that will work. Otherwise
In AutoCAD Land Desktop, at the command line, enter options.
In the Options dialog box, Files tab, expand Support File Search Path.
Mark sure none of these are missing, (the last 3 only apply if you have Raster Design):
C:\Documents and Settings\user\Application Data’Autodesk\LDC2009\R1 7.2\enu\support
C:\Program Files\AutoCAD Civil 3D Land Desktop Companion 2009\support
C:\Program Files\AutoCAD Civil 3D Land Desktop Companion 2009\fonts
C:\Program Files\AutoCAD Civil 3D Land Desktop Companion 2009\help
C:\Program Files\AutoCAD Civil 3D Land Desktop Companion 2009\express
C:\Program Files\AutoCAD Civil 3D Land Desktop Companion 2009\support\color
C:\Program Files\AutoCAD Civil 3D Land Desktop Companion 2009\land
C:\Documents and Settings\user\Local Settings\Application Data\Autodesk\LDC2009\R1 7.2\enu\Support\
C:\Program Files\AutoCAD\ Civil 3D Land Desktop Companion 2009\FDO\bin
C:\Program Files\Common Files\Autodesk Shared\AxUi
C:\Program Files\AutoCAD Civil 3D Land Desktop Companion 2009\civil
C:\Program Files\Raster Design 2009\OE
C:\Program Files\AutoCAD\Raster Design 2009\Help
C:\Program Files\AutoCAD \Raster Design 2009\Support
If this doesn't fix it, I have a work around. When you first open a drawing, before you do anything else, the very first command should be specific to the application you usually use. I use Land Desktop Companion, so I start a command from the Points or Terrain menu, the application will initialize and all the commands will work as usual for that drawing session.