if you use the SQLServer driver, connection string is like:
Server=myServerAddress;Database=myDatabase;Trusted_Connection=True

to test a login, the best is to use the 'Test a login' property in the Configuration->Configure Web Security dialog.
you can change the user name and password.

Your script is incorrect and does not even compile, here is a sample that should work:

Hello,

I have problem with database authentication.

I opened seal server manager, from Configuration=> configure web security I set the security provider to database authentication after that I set the use custom security script to true and I write the code below in the script:

@using System.Data
@using System.Data.Common
@using System.Data.SqlClient
@using Seal.Helpers
@{

SecurityUser user = Model;
string connectionString = "Provider=SQLOLEDB.1;Persist Security Info=False;Initial Catalog=MyDatabaseName;Data Source='My server's Ip address'";
SqlConnection connection = new SqlConnection(connectionString);
connection.Open();
SqlCommand command = new SqlCommand("SELECT dbo.UserGroups.UserGroupName FROM dbo.UserGroups INNER JOIN dbo.Users ON dbo.UserGroups.UserGroupId = dbo.Users.UserGroupId WHERE (dbo.Users.UserName = {0}) AND (dbo.Users.Password = {1}) , Helper.QuoteSingle(user.WebUserName), Helper.QuoteSingle(user.WebPassword)",connection);

object group = command.ExecuteScalar();

if (group != null && group != DBNull.Value)
{
user.AddSecurityGroup((string)group);
}
else
{
user.Error = "User unknown from the database.";
}

}

I have a database in Sql server, when testing it with my user information in the database through Test a login, I got an error :

ERROR: Authentication failed
User login name: Admin

Error:
Keyword not supported: 'provider'.

what should I do to solve this problem?

Would you please help me with this as soon as possible?

Thanks in advance,
Aynaz