Below are the common things that could be considered bugs.

fails to start 

Check that you have a 1.6 VM. Either by using java-version-test.jar in the folder or by going to  http://java.com/en/download/installed.jsp (That may not be accurate, it is dependant on a working browser plugin)

Otherwise please send the log file. 

Stack traces

If you sometimes take a look at the console, you will notice Stack traces from time to time. Not all of these are worth mentioning, so here are some tips.

This is a stack trace:

Uncaught Exception in AWT-EventQueue-1: java.lang.IndexOutOfBoundsException: Invalid index
                 org.tcpfile.gui.CustomEventQueue.dispatchEvent(CustomEventQueue.java:42)

This one is a known bug, it comes up only if you have the queue tab open, it is no problem.

However, it usually says either Uncaught Exception or Caught Exception. All Exceptions that say Caught dont interest us, since they are caught. So report the Uncaught Exceptions if they are not already listed on the site.

So in short: 

1. Dont report caught exceptions
2. Dont report exceptions we know about (List will follow)

How to report a bug

After you have read the appropriate paragraph, proceed like this: 

All bug reports over the sourceforge bug tracker