The tutorial states:

CLR EN
SETB EN
MOV DATA,#28h
CLR EN

Where it *SHOULD* be

CLR EN
MOV DATA,#28h
SETB EN
CLR EN

The problem is, according to the tutorial, it's trying to enable a command before the command is present on the port! Actually, I like to put nops between the setb en & clr en, just to be sure it has time to read, but it should work either way.
Hope this helps :)