Shutdown wallet. Open %appdata% folder and find nevacoin. Remove everything except wallet.dat (this is your wallet and coins) and power wallet back on and wait for resync.

Wheere is appdata: https://en.bitcoin.it/wiki/Data_directory (just replace bitcoin with nevacoin)

Latest release 1.4 https://github.com/Nevacoin/nevacoin/releases/tag/v1.4.0