Can I go back to Feathercoin-Qt version 0.6.4.4 once I upgrade to Feathercoin-Qt 0.8.5?

No, there is no automatic mechanism to revert versions back.

Your wallet.dat may be corrupt.

It is possible to dump your private keys and import them back into a regenerated wallet.dat

First - "Export" your Receive addresses & descriptions to *.csv text file, for information if required.

The private keys do not store a description.

Go to the console in the Qt client Help and do the following.

If you've encrypted your wallet you'll need to unlock it

You may be able to export and re-import your keys but moving backwards a version is not recommended or tested.

If you've encrypted your wallet you'll need to unlock it

walletpassphrase [passphrase] 1000

Then enter in dumpprivkey and your public address. This will generate the private key for your public key, make a note of this key.

dumpprivkey [feathercoin address]

Once you have all the private keys exported close the client down, backup and remove your wallet.dat from the Feathercoin datadir. Run the program to generate a new wallet.dat and then run the following to import your private keys.

importprivkey [feathercoin private key]

The client will freeze a little while it rescans the blockchain. Once all keys have been imported you will have a brand new shiny wallet.dat file ready to import to 0.8.5.

Error -4 - If you see error -4 when exporting your private keys, it means the Password timer has run out.

Your wallet.dat may be corrupt. 2

After backing up.

Try -salvagewallet

command line option introduced after 0.7 versions of protocol.

What is the upgrade procedure to Feathercoin-Qt 0.8.5?

Feathercoin 0.8.5 contains a number of enhancements, which means it is not possible to go back to version 0.6.4.4, once the upgrade procedure has been completed.

It is possible to simply import an old back-up, from v0.6.4.4 to v0.8.5 and that is being tested currently.

A Feathercoin procedure for upgrade is currently being reviewed by Staff as it is an important part of the release procedure for feathercoin-Qt v0.8.5.

It is well known that the Bitcoin core wallet (0.8.5) does not scale to a large number of transactions.

Litecoin and Feathercoin are using the same code and has the same problem. Small scale vendors can workaround this problem by periodically replacing the wallet with a smaller wallet with empty addresses and old transactions removed. Large scale vendors currently use their own proprietary implementations to replace the reference wallet, usually as a private competitive advantage.. There is work in the next year to hopefully improve the scalability of the reference implementation. (0.9)

What is the Bitcoind or Feathercoind Debug.log?

Currently, even the release version of the Qt wallet or daemon creates and updates a Debug.log file. There is no limiting factor to that file so if you are running as a server, you may need to take occasional action to clean up that file or do so automatically.

This may also become an issue for merchants running wallets for long periods, in the future.

http://bitcoin.stackexchange.com/questions/18857/how-to-limit-the-debug-log-file-while-running-bitcoind

When I use the RPC command, I have a errors.

feathercoind getrawtransaction "f3c78bfeeafc01bb398542dde2ea4fc0296d8091065c600688ed2bb1f0eded42" "1"

error: {"code":-5,"message":"No information available about transaction"}

How to previous output from Raw transaction ?

Put "txindex=1" into your feathercoin.conf, then restart the client with -reindex.

Normally, the client indexes only transactions related to your wallet's addresses, to conserve some diskspace. With txindex=1 it will build a full transaction index.

Is there a virus in the Blockchain?

I ran clamav or avast virus scanner and got these anomolous results, what should I do?

/home/user/.bitcoin/chainstate/276605.sst: Chren-4016 FOUND
/home/user/.bitcoin/chainstate/276482.sst: Gen.805 FOUND
/home/user/.bitcoin/chainstate/276603.sst: Italian.1 FOUND
/home/user/.bitcoin/chainstate/276678.sst: Boot.Gen.10past3 FOUND
/home/user/.bitcoin/chainstate/276615.sst: Stoned.1 FOUND
/home/user/.bitcoin/chainstate/276526.sst: Gergana.9 FOUND
/home/user/.bitcoin/chainstate/276488.sst: Vienna-645.A FOUND
/home/user/.bitcoin/chainstate/276506.sst: Peace.1 FOUND

These are known false positive virus signatures in the Bitcoin chainstate. They are never run, so should not be a problem. They may have been deliverately inserted by a "joker". However, always investigate any virus reports.

https://bitcointalk.org/index.php?topic=581432.0

https://bitcointa.lk/threads/security-dos-vulnerability.293399/