Issuing 2 selects on the same connection without reading all the result-set is deemed to be having "multiple active connections".
DBD::ODBC does support multiple active statements.
Microsoft SQL Server did not used to support multiple active statements. There were tricks you could play that allowed you to use multiple active statements but they came at a cost. Read the DBD::ODBC pod which explains some of these tricks and why they could cause you problems.
If you have a newer SQL Server you can add "MARS_Connection=Yes" to your connection string and you will get multiple active statements. Here again, read the DBD::ODBC pod and FAQs.