what is this error?

[Mouse droidz 21]

today i was hosting and no one was on my server, i loaded a build and then i get some error i dont know anything about. can someone tell me what the forget is this error? it pissed me off...

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[Plexious]

Does this happen often?

[ContrabassDrio]

I got that once, but I reset blockland and it never appeared again.