How does it seem "but it looks like this method never succeeds" so, are you getting any error messages ?
It has been some time since I tried an upload from quarantine, so I don't know if there is any screen acknowledgement it has been uploaded successfully.
It would have been handy if you posted a link to the VT results, as you haven't given any real details (file, program name, etc.) so it is very hard to help.