I could not do this. I backed up the wallet, saved the keys, but did not enable the option to send the coins.
Just when I create a new wallet, I get the send option is available for this new wallet, which by the way is empty. When I opening the old wallet, it is still impossible to withdraw.
You could try from command line and import your old wallet using your keys.
See this:
https://www.youtube.com/watch?v=FWMMoGJSl04It is for other coin but the process is similar to that.
When using command line wallet you must have a daemon started, this is for Linux but the same thing should work for windows (using windows apps of course) and then the daemon (walletd or something that ends with d) must sync the entire blockchain. And then in other window you launch command line wallet and import the old one using your keys (as in this video).
The simplewallet.exe not reconize the arg --generate-from-keys.
