Java Database Connectivity (JDBC)

We are running 3 webservers, all are Dual PIII, NT4 sp6a machines. All machines run a Tomcat webserver and One machine hosts a SQL server database as well. The two machines that do not host the SQL server database frequently (but intermittently) report the following error when trying to connect to the SQL server machine. The machine that hosts the SQL server (and is most heavily used) does not report the problem.

java.sql.SQLException: [AVEConnect][JDBC SQL Server Driver] Address already in use: connect
at net.avenir.jdbc2.x.<init>(Unknown Source)
at net.avenir.jdbc2.Driver.connect(Driver.java:399)
at java.sql.DriverManager.getConnection(DriverManager.java:512)
at java.sql.DriverManager.getConnection(DriverManager.java:140)

Nothing strange appears in netstat and there are very few connections established or in TIME_WAIT on the problem machines compared to the OK machine.
Port scans also show that there are no hanging connections blocking port 1433.
The problem occurs whether the connection is across the firewall or not.
Nothing is entered in any log indicating a system or application problem and there are no processes blocking the call in SQL server.

I'm stumped, any ideas?

Thanks.