postgresql error while connecting to cluster with pgadmin

i have created two cluster in the same host the first called "main" with
port 5432 the second called "remote" with port 5433.
but when i try to connect with pgadmin3 to the second cluster i get the
error "authentication failed".
if i try to connect to the first cluster i don't have any kind of problem.

i'm using postgresql 9.1 and ubuntu 10.04