Remember to update your XDN from https://github.com/xdn-project/digitalnote/releases DigitalNote v4.0.1-beta
This version has an increased default block size limit to 200kb.
Poloniex is using an outdated software (like they always do), they should update it and there will be no problems at all.
In future try to avoid Poloniex for trading XDN-project coins.