Vuze error message

I have downloaded Vuze plus and have started to download music through Isohunt. I managed to download a few files but now none of my new ones will download and I keep getting the error message ‘Failed to establish listen on port UDP:59607. Check that other applications aren’t already using this port. Also check for another copy of Vuze running’.
I have already checked in task manager and I only have one copy of Vuze running. In real simple terms, what does that mean and how can I fix it??? Thanks!