severino trouble

Hello all, i have similar type of problem. i have arduino severino board with atmega328p with serial connectivity. i got preloaded "Blink" prgram on chip which is working good. but when i try to upload new sketch it gives msg:

avrdude: stk500_getsync(): not in sync: resp=0x00 avrdude: stk500_disable(): protocol error, expect=0x14, resp=0x51

i have selected correct board type and com port. please help