I did re-download blockchain files first (removed files in AppData/Roaming/intensecoin/DB) and it worked.

Also had this problem again with another wallet, and GUI(File>Reset wallet) also worked, which is obviously a lot faster than downloading blockchain again.

Thanks for your help, people.

I wonder what caused this. I had enough free space on system drive.

It says "Wallet synchronized" though.
Does not look like anything changes.
How can I force it to sync?

I had 2000 coins on a wallet.
After restarting the wallet today, balance only shows 6 coins from last transaction, all previous transactions are marked as "cancelled".
Can someone explain this?
Using version 1.4.1.