First, be sure to use the newest version of the wallet available from dash.org/downloads.
In order to rebuild your node's blockchain, you'll have to add "reindex=1" to dash.conf and then restart the Dash wallet. It will reindex the inconsistent database, and then once fully synchronized, your wallet will be fully operational again.
After you've completed the previous steps, remove the "reindex=1" line from dash.conf to avoid reindexing on every wallet startup.
You can find the dash.conf file and DashCore's wallet folder at the location shown in the table below (on Mac you might need to use the combination of command+shift+dot to show hidden folders).
If you still have the issue after following these steps, please contact us via support@dash.org