Dear Melinda Morang,
Thanks for the reply. No i didn't delete the system junction shapefile.
Actually in the final step , after the new network shapefiles have been created, i try to build the network but it always failed and gives me this error.
Also, i have tried these tutorials using my personal Laptop (ArcGIS 10.1 , Windows 7, service pack 1), and there is no such error.