It's a hammered tourist token from the bank's open to the public days. I believe it happens yearly. The bank there, distributes collector coins, banknotes and on those days they have tours, displays, etc. I don't think it's much of an error. Just put it on mute...
What is a little strange is those "strike-out" lines. Basically you see the text "Polskiej bankowości centralnej" (Polish central banking) at the top, and "180 lat" (180 years) at the bottom. On the other side it says "2008 dni otwarte NBP" (2008 NBP open days). And yes, the central bank has those open days every year, in various cities. The 180th anniversary refers to when the first Bank of Poland was established (1828). Today the name of the Polish central bank is "Narodowy Bank Polski", hence the NBP. Christian
