Run the application from the server's console. Do the exact same steps that lock up the published application. If it locks up the console, you can be 90% sure it is the application itself. Before you rule out Citrix, the application, or anything else, it is best to find a procedure of steps that reliably locks up the application. Without that, it will be MUCH harder to identify. Once you have gotten a good failure procedure, check out filemon.exe and regmon.exe. Run either of them while you do your procedure, and they can provide clues to what is causing the failure. There are freeware version available from sysinternals.com.