Hey there,
The best fix I've found is often as simple as uninstalling and reinstalling Overwolf. Sometimes the client gets caught during the launch sequence and consequently a clean cache and install helps establish a cleaner hook up. Other than that it's hard to know specifically whats wrong without seeing the log files. I'd suggest sending an email to support@overwolf.com with your log files.
http://feedback.overwolf.com/knowledgebase/articles/356475-how-to-sending-logs
Thanks!