Help erasing in a sequence!!!

Hi Guys, i am having a problem... i recorded a beat in my mpc1000 (jj os1) and all goes fine (2 bar sequence).. but in the moment i wanted to erase from the a sound from the current sequence of a pad i found a problem!! i think that the machine is only erasing things in the second bar, but not in the first one !!! i tried overdibbing while holding erase + pad.. and in the erase window too, and nothing happened :S

pls HELP !!!

PS: i bought the machine a few days ago, so maybe i am doing something wrong...