There are two ways to sort this problem, both of which are effectively making a clean install of Frostwire.
If you are using Windows:
1. Fully close Frostwire. Go to start > run and type in %appdata% this will bring up a number of preference folders among which will be FrostWire5. Delete this folder and restart Frostwire and reconfigure it. I strongly advise leaving the Torrent Data folder left as the default.
2. Completely remove all traces of Frostwire5. To do this use Revo Uninstaller
or a similar program since Windows uninstaller in the Control Panel fails to do the job thoroughly. Revo will locate additional related files which need to be removed.
Before doing this ensure you have a back up of the files in your save, shared Torrent Data and Torrents folders, or at least remove them to your desktop or somewhere similar, just to be on the safe side.
Then install Frostwire from the FrostWire.com link above.
I hope this helps. If you do not have Windows or need more help please post back with details.