Java HotSpot Virtual Machine

Currently I'm working on calling a C program from Java using JNI. I've created the dll file without any difficulties and no warnings are been given in its creation. However when I try and load the file in the Java program the program hangs. From what I've read this is due to a problem with the dll. However I am unsure how to debug a dll. How is this done?

For extra information the dll was created using cygwin under windows. The created dll was developed in such a way that it doesn't depend on cygwin.

Any help would be much appreciated.

Thanks
- Martin