Must be using 2.1 or higher if a bootstrap file was used. We’re still working out issues with 2.1 so it’s better to stick with 2.0.3 for now @ghost. Which you can find on our main website nubits.com/download
Before doing anything please back up your wallet files.
https://docs.nubits.com/performing-backups/
After that you can clear out the contents of your data directory to have it sync from scratch. You can use the guide below to find your data dir.
https://docs.nubits.com/creating-conf-file/#find-the-nu-data-directory
Make sure to shutdown the wallet first. Then you can delete everything in the folder except for wallets.dat, walletb.dat and nu.conf if you have one. When you start up the client it should begin downloading blocks from peers.