probably a long way around, but the fix I found was to go to computer>local disk C>Users>''username''>AppData>Roaming>
Then open fastcoin folder, then open blocks folder, then delete the last .dat file
I was then able to open the wallet without the error meesage, but had to click ok to download the whole blockchain again. my wallet is now ''reindexing blocks on disk''.around with this,
For any noobs like me playing around with this, you should obviously do the back-ups first with any issues, especially back-up of the wallet.dat file
