Every now and then when I build my solution here (with 7 projects in it) I get the dreaded \'Command copy exited with code 4\' error, in Visual Studio 2010 Premium ed.
To expand on rhughes answer,
The robocopy works beautifully, just incase you need to include sub directories you can use /e
to include subs and copy empty directories or /s
to include subs excluding empty directories.
Also robocopy will report back a few things like if new files were copied, this will cause VS to complain since anything above 0 is a failure and robocopy will return 1 if new files have been found. Its worth to mention that robocopy first compares the Source/Dest and only copies the updated/new files.
To get around this use:
(robocopy "$(SolutionDir)Solution Items\References\*.dll" "$(TargetDir)") ^& IF %ERRORLEVEL% LEQ 4 exit /B 0