What kind of error is this?
link
In the middle of "2" from 20 you can see an fragment from the meridians of the coat of arms from the other side. Also some sun rays are visible. These are in relief.

It looks like a die clash to me. This is a very interesting anomaly that occasionally happens with all sorts of coins, but it is probably not enough of an error to qualify as a special type or category of its own (an overdate, for example, might be such an error).

banivechi, I looked at the reverse again and it looks like there might be clashing on the sun at the bottom from the obverse "KOP" letters -- I'm not sure, though.

Good find, by the way!

Scan is poor in details. Afternoon I will try to make some photos. If the light come tangential more details are visible. At a 20 x magnification the whole globe can be identified, the contour of the sun also and many rays.

Definately die clash there. Nice coin you got there Banivechi!