cant back up pda with activsync

hi there i have on purpose turned the power off on my pda and erased the sd card,
i have then tried to re put back onto the pda my backup copy with is done by activesync and it then baiscly cant remember message now it was gone 1.30 am in the morning, but it wouldnt do it anyway,
is there some thing i did wrong,
i went into activesync and pressed on backup to pda and then it didnt like it due to the name on the backup???? so i then called the pda the name first and it said that name already in use????
thanks for now.