Important update (update is mandatory)1:
very very important backup the
wallet.dat and
backups file(the file in /Roaming/masternodecoin/** )
if you do not backup the wallet.dat and backups file ,you will loss all MTNC
2: delete the whole blockchain data and peer.dat and others file and MTNC client file
3:down load the new client MTNC V2.1.0.0 version as below link (windows) ,linux and mac version you should complie yourself
if you dont want to wait for sync ,you can download blockchain data as below (2018 03 21)
4: open the new client MTNC V2.1.0.0 then close the client
5: put your wallet.dat to the file (the file in /Roaming/masternodecoin/** )
6: then open the client again
7: set up masternode follow the guide (the link
https://docs.google.com/document/d/11WnHDlVmNCTZDnrn8yQYXE21PRBn8h6A5bQiaVpn6Ts/edit?usp=sharing)

Second soure link : MTNC Windows client V2.1.0.0 MTNC Blockchain data source 2018 03 21