mul instruction

Thank you very much for your valuable suggestion,as per your suggestion i have done the changes in my program given below but still i am getting the same error(This register combination results in UNPREDICTABLE behaviour)
area thu,code
entry
THUMB mov r1,#0x02 mov r2,#0x02 mul r1,r2 mov r3,r1;store result in other register
loop b loop
end

so i kindly request you to do the correction in my program above...

Thank you very much for your valuable suggestion,as per your suggestion i have done the changes in my program given below but still i am getting the same error(This register combination results in UNPREDICTABLE behaviour)
area thu,code
entry
THUMB mov r1,#0x02 mov r2,#0x02 mul r1,r2 mov r3,r1;store result in other register
loop b loop
end

so i kindly request you to do the correction in my program above...

Have you looked up the MUL instruction in the Assembler Manual

http://www.keil.com/support/man/docs/armasm/armasm_cihihggj.htm

Note that there is a restriction stated there on which registers may be used in the Thumb instruction...

Have you looked at the ARM Architecture Reference materials?
infocenter.arm.com/.../index.jsp

My previous answer was wrong. That restriction is not for your case :)
I don't know which uC do you use and I cannot test right now, but try using
MULS r1,r2,r1
instead of MUL r1,r2
and see if that works

i am using lpc2129,and muls r0,r1,r2 is an arm instruction not thumb

If you have made an effort to read what Andy Neil suggested:
http://www.keil.com/support/man/docs/armasm/armasm_cihihggj.htm
you would read this:

Thumb instructions

The following form of the MUL instruction is available in pre-Thumb-2 Thumb code, and is a 16-bit instruction when used in Thumb-2 code:

MULS Rd, Rn, Rd
Rd and Rn must both be Lo registers.

LPC2129 is ARM7TDMI-S based which is pre-Thumb-2.

And the instruction is MULS R1,R2,R1 (do you see the difference?)
where R1 is also your destination register

Yes, that is what I was hinting at when I said,

"Note that there is a restriction stated there on which registers may be used in the Thumb instruction..."