Table creation with h2 database

I am new to h2.I just using h2 in spring embedded mode with hibernate.I am trying to execute the following scripts using h2.

CREATE TABLE acct_authority (
  id bigint(20) NOT NULL auto_increment,
  name varchar(255) NOT NULL default '',
  value varchar(255) NOT NULL,
  PRIMARY KEY  (id),
  UNIQUE KEY name (name)
);

The table acct_authority is created without any error.But if i create another table with the following script.

CREATE TABLE acct_role (
  id bigint(20) NOT NULL auto_increment,
  name varchar(255) NOT NULL default '',
  PRIMARY KEY  (id),
  UNIQUE KEY name (name)
);

It shows error as constraint name allready exists.What mistake i did.