Can't name my account

I'm new to PBE server and when I logged into my account, I can't name my account. On naming window, after entering name and clike "start now", I got this error:"Name currently unavailable, Enter a new name and try again". I have tried 20+ names that nobody should picked like "dhofh32kan2" or "dnsoncuxa231dds" but still got this error.
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