Try "Tools/Restore Backups" and see if that helps. If it doesn't, re-installing Freelancer should do the trick. I've gotten similar reports in the past about a username/password error, but have no idea what causes it - why would the game ask for a username and password in the first place?
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Freelancer Mod Manager: newbies' dreams come true
Belief in Jesus: the only way to Heaven
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Freelancer Mod Manager: newbies' dreams come true
Belief in Jesus: the only way to Heaven