In case of any problem you have encountered with Monero:
1. Backup your wallet.* files.
2. Delete ALL Monero files from your computer.
3. Download 64-bit Monero zip & blockchain.bin from 1st sticky page of this thread.
4. Unzip & place all the files downloaded above to the directory: "C:\Users\
5. From the backup made at step 1, place wallet.* files ||| EXCEPT wallet.bin ||| into directory at step 4.
6. Start bitmonerod.exe and wait for it to sync with the net.
7. Start simplewallet by the commad prompt: "simplewallet --wallet-file wallet.bin" (name of file that must NOT exist in directory at step 4).
8. When you want to stop any monero executables - ALWAYS type "exit" & be patient.
simplewallet re-creates correct version of wallet.bin for you.
Since you migrate to 64-bit Monero by CORRECT WAY mentioned above - you will never have any problem except being patient due to Monero is currently somewhat slow.
Monero developers are working hard to entirely fix the problem - you may choose either migrate the way I described above, or wait for developers to release a fix.