[Help] WabboCMS - Register

I use the database (.sql file), that is released in the CMS (WabboCMS), but i have an error? ... It's not a real error but, more a exploit. When i will register, "Username: testingone is taken!" But the table, "users", is empty? Screenshot by Lightshot

Sorry for my bad English, i'm from The Netherlands, and thats why i speak not so good English.
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Nobody? Can nobody help me?