External mode in simulink?

Currently I am using usb 6009 daq board for data acquisition in using simulink. I have created a model with taking analog input from data acquisition toolbox. Then when i want to run in external mode and try to connet to target, the following error is coming up:

Could not execute target data map file 'untitled_rtwin_win32\untitled_targ_data_map' or it does not exist. Stop the target, delete the untitled executable, rebuild the code,and try again. Note that execution of external mode requires the build directory to be present...

How can I solve this problem? For your info, I am using 32-bit matlab, version: 2012a,

Any help would be appreciated Thanks