Try this. Read all steps first. You probably have client v0.6.3. You need 0.6.4. I just did this for my FTC wallet 10 minutes ago with success. This procedure should work for updating any coins' client, and should fix a corrupted blockchain. All these precautions are intended to prevent you from deleting or moving an important file mentioned below.
0.) Don't empty your recycling bin until your FTC update is complete and successful (fatfinger precaution).
1.) Delete the Feathercoin folder (.exe file, some .dll's, text files). This folder was included in your original client's zip file.
2.) Delete everything in the FeatherCoin AppData folder **BUT NOT the "wallet.dat" file!!!** Leave the folder and the wallet.dat file, and if you've made a Feathercoin.conf file you can leave that in there too. Just don't delete the wallet.dat file. This folder is probably located C:\Users\(you)\AppData\Roaming\FeatherCoin. The folder "AppData" is hidden - enable "show hidden files" to access it.
3.) Download and run (assuming windows)
http://github.com/FeatherCoin/Feathercoin-Clients/raw/master/feathercoinqt-win-0.6.4.1.zip. This is v0.6.4 from the FTC homepage 6/14/2013.
You're done! If you've reinstalled without bothering the original wallet.dat file, you should have all your addresses as they were, and the blockchain will re-download.
