Delete FW's preferences folder when FW is properly closed... more info here:
FrostWire - Permissions Error?
And for extra info about how to find the prefs folder, check out this thread:
LimeWire Pref Folder in Vista
The info there refers to LimeWire (LW) but info's the same for FW
Deleting the prefs folder will revert all settings within tools > options to default, so you'll need to go back through tools > options afterwards & reset things
If you're not sure of your settings, go through & make a note of them before deleting the folder.