Not sure why that's happening. We had one other report of that on a Windows based server, but that doesn't seem to be your case.
Either way, to install manually, you simply need to unzip the com_jfbconnect_xxxx.tar.gz file to your local system. Then, in the /admin/packages folder, you'll see the system, user, authentication, content plugins and login module. You'll need to install each one manually from there instead of letting our main component try to do it automatically.
Definitely hope this helps, and sorry for the inconvenience. We haven't been able to diagnose the problem fully to understand the cause. It seems to be some sort of permissions issue, but just haven't been able to recreate it.
Please let us know how your experience goes, and good luck,
Alex