You noted:
Please enter a valid username. No spaces, at least 2 characters and must contain the following characters: <> "%; () &.
Is that correct that those special characters *must* be in the username? If so, that would explain why first.last works (alex.andreae) but firlas (aleand) does not.. it's missing the period.
As for the 404 error page, can you tell me:
* What the username that JFBConnect creates is
* What the URL that generates the 404 error is
* What you expect the URL to be
* Are you using any SEF extensions on your site, or just enabling SEF URLs in the Joomla Global Configuration area
You don't have to include the domain, just the path to the profile page.
Finally, if you go to the profile URL you expect to work (vincendozi-cicco), does that work?
I'm unsure what's going on, but we'll gladly help however we can.
Thanks,
Alex