The full FTP log, also with it set to Debug mode might, reveal some details that help see what's happening.
To open the log in Debug mode:
- Enable the Debug option in the FTP address book (on the Display tab when editing an FTP address book item or the Default Settings item).
- Select the FTP / Display FTP Logs menu item, then select either [All Activity] or the specific site you care about from the drop-down list of logs.
Is it possible your firewall(s) may be blocking Opus but not the other clients you have tried?
Another possibility is the server requires an encryption protocol which Opus doesn't currently support, and won't allow fall-back to the ones Opus does support. The logs usually indicate this at the start of the connection, before any folder listing has been transferred,
There are no known issues with ESET Smart Security and no similar reports from other people about that. If you have crash dumps, you can zip and email them to email@example.com and I'll see if it indicates which component might be causing the problem. These Other Troubleshooting section of the FAQs also has several guides for tracking down crashes, which may help. The most suitable guide will depend on when the crash happens.