What's the DBD and what are the contents of $dbname? Standard syntax (at least since I started using DBI) is:

my $dbh = DBI->connect("DBI:ODBC:test_connection", $user, $passs, {opt
+ions});
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So the first argument to connect is a connect string that includes the driver (DBD), as well as the specific connection (e.g. ODBC DSN, Oracle DBN, etc.). That appears to be the difference between "current" semantics and what you're using.