Fail to force dirsync,

I recently launch a dirsync lab. Automatically ad-sync works fine, but, when turn to force sync using shell. Error happen:

"user is not a member of the local administrators group on computer"

actually I think I have add the user into the local group..........

Can you guys help me solve this issue?  Or, Firstly, show me how to add user to a local admin group if I not do the local group adding ?

thanks.