Connecting Matlab r2011 with external device/machine.

When i try to connect simulink to external device i get this error please help if any one can?

Could not execute target data map file 'ball_grt_rtw\ball_targ_data_map' or it does not exist. Stop the target, delete the ball executable, rebuild the code, and try again. Note that execution of external mode requires the build directory to be present.