Alessandro,
The problem is because you've already added the index to the table. Please see your previous post from back in January:
www.sourcecoast.com/forums/jfbconnect/jf...red-providers#p56326
Since you added the index manually, the database is throwing an error because a duplicate index can't be added. I'd suggest deleting the index you created and then upgrading JFBConnect. The index will be re-created and things should be good to go. You could also modify our installation package to remove the index creation, but that is a little more detailed. If that's what you'd prefer though, please let us know and we can guide you through that.
Also, just to note, the index is not set to be unique. There can be many entries in the j_user_id column with the same id, they are just indexed for a faster lookup.
I hope that helps, but if you need anything else, please let us know.
Thanks,
Alex