Change your code to
MOV R0, #IDATALEN-2 and try it again.
WHY, WHY, WHY - there is an absolutely fine piece of code supplied by Keil. No need to change anything, just use the supplied.

Why, oh why, does Raj screw around with startup.a51 when Raj states he is new to C. He will find many other things to wonder about long before (if ever) he need to wonder about startup.a51. Mucking with startup.a51 for a beginner in C is the equivalent of taking the engine in your car apart before you know how to change a tire.

Erik