Funny errors: pre-dates British use of Gregorian calendar

[Boboss]

In my apache error logs under /usr/local/apache/logs/error_log, I see funny errors, plenty of them, that say:

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warning: pre-dates British use of Gregorian calendar
warning: pre-dates British use of Gregorian calendar
warning: pre-dates British use of Gregorian calendar
warning: pre-dates British use of Gregorian calendar
warning: pre-dates British use of Gregorian calendar
warning: pre-dates British use of Gregorian calendar
warning: pre-dates British use of Gregorian calendar
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Question is: how do I get rid of this, and what is it?