It could be due to I started the masternode first through command prompt of interzoned & interzone-cli, then stop interzone-cli & open windows qt wallet
This seems to be true.
I started my MN via the interzone.conf settings, by adding the following lines:
masternode=1
masternodeaddr=[[IP-OF-MASTERNODE]]:55675
masternodeprivkey=[[PRIVATE-KEY]]
Then close the wallet, configure your masternode.conf file and start the wallet.
Maybe the wallet will crash if the configured masternode (in your masternode.conf) is not in the list of Masternodes yet. As once it has been started it's working fine.