Java Database Connectivity (JDBC)

I'm having a very weird problem. I have a utility Informix connection class which I've used numerous times in the past in various Eclipse projects which deployed using FatJar and never had a single client with issues. Most recently I used it in a NetBeans project and tried to distribute it with the application in a jar file and the libraries in a lib directory. The problem I'm having is that on some clients, it refuses to connect to the database server while on other clients it works fine.

1. All clients are on the same LAN.
2. All clients are running Windows XP w/ latest SP or Windows 2003 Server.
3. All clients connect succesfully using identical connection criteria in ODBC data source.
4. On bad clients, the only error I get is the one below. No class not found errors or any other errors at all. All other aspects of the application work fine. They just timeout.

On the clients where the problem exists, the connection simply times out and I get a this error:

java.sql.SQLException: com.informix.asf.IfxASFException: Attempt to connect to database server (<server_name>) failed.

Which normally means an address or port issue with the connection string. However, the exact same compile code runs fine on about half of the dozen clients I've tried. There is no commonality between the working clients (multiple OS versions, different levels of JRE installs including some that were brand new installs). At first I thought it was maybe a classpath issue, but on two of the working clients there is no classpath set.

Also, to be sure they were all running the exact same code, the JAR files and libraries were put on a network share and the program was run directly from the shared folder.

At this point I'm completely baffled. I have no idea what to check next or where else I can look for help. This is really just a shot in the dark but I'm hoping someone has seen something like this and can give me some ideas on how to continue my troubleshooting.

Thanks,
Pablo