Thanks!

In Yenten 3.1.0, it's programmed that the algorithm will be changed on and after UnixTime 155390400, i.e. 2019-March-30 00:00:00 (UTC).
https://github.com/yentencoin/yenten/blob/master/src/hash/yespower/yespower.c#L41

The exchanges, Graviex and Crex24 are Yenten 3.1.0 ready, and TradeSatoshi will be soon.
Please update your wallet to 3.1.0!
https://github.com/yentencoin/yenten/releases/tag/3.1.0
(As usual, it's good thing that back up your wallet.dat before updating.)