mapping error

[little83]

dear all

I got the follwoing error while trying to create database user

The role ''db_owner'' does not exist in the current database.
Changed database context to 'try2'.

here the code

[code]
string query = string.Format("CREATE DATABASE [{0}]", textBox5.Text.ToString());
string query1 = string.Format(" CREATE LOGIN [{0}] WITH PASSWORD = '{1}' , CHECK_EXPIRATION=ON, CHECK_POLICY=ON ", textBox6.Text.ToString(), textBox7.Text.ToString());
string query2 = string.Format(" USE [{0}] CREATE USER [{1}] for LOGIN [{1}]", textBox5.Text.ToString(), textBox6.Text.ToString());
string query3 = string.Format("USE [{0}]; exec sp_addrolemember ['db_owner'], ['{1}'];", textBox5.Text.ToString(), textBox6.Text.ToString());
[\CODE]

Any ideas?