OK...first off, let's stick with the Documents directory for the time being. Dropbox shouldn't be an issue, but let's work with one variable at a time.
I was assuming given the thread you posted in that you're getting the splash screen when you double click on HD6.jar (indicating the HD is loading)...and that it's getting stuck right around the "Loading Plugins..." point.
If that is the case, do you show a file "trace.log" in the directory that you're running from after the problem occurs? If so, please post the contents of that file in a follow-up.
If you are _not_ getting the splash screen then you're not having the same issue noted in this thread and I'll need more details. What is happening when you double-click HD6.jar (details needed)? What happens if you open a command prompt, cd to the directory that you unpacked HD into, and enter the following:
java -jar HD6.jar
Post the output of that command in a follow-up.