I don't think this is a DBI problem. If you post a larger chunk of the script I'll be able to tell you more. It looks like there might be a limit on the number of connections the Server allows or the Server is overloaded. If you're not on a production system, you can try killing some processes before you run your code again.

In MS SQL you can run the sp_who stored procedure to see the current activities in the dB. You can use the kill command to stop them.