unable to access the computer access denied

2 Pcs A & B runing under windows xp sp2, on peer tp peer network (workgroup). I can brwose computers fron each side, but when i want to manage B from A (start -}Run -}type mmc -} file -} add/remove snap-in -} add -} local users and group -}another computer -} computer B : unable to access the computer access denied
both computer A-B adminstrators