I would try switching back to Bitcoin 8.4 client, but I am extremely hesitant to even touch it after what I just went through. Bare in mind, I wrote the passphrase out in plaintext in textedit and analyzed every single pixel (it's only 8 characters!). I copied/pasted. Nothing. Nothing worked on 8.4.
Imagine.. 90% of my life savings are in there, so I just experienced the closest thing to a severe panic attack.
Perhaps you should also go to this website
https://www.grc.com/haystack.htm and input a password of the same length and character type (although not obviously your exact password) into the box to see somerought stats on how difficult it is to be brute-forced. Not too difficult I would imagine, and now remember that some in this community will have GPU farms not mining much BTC anymore, which could possibly earn more in more 'malicious' ways...
Also, bare in mind that if you have used any dictionary words, or dictionary words with number/char substitutions (e.g. pa$$w0rd) then this just became a whole lot less secure.
Now, you have just advised everyone that you have backups and a weak password. I have no idea (not that computer literate at a code level myself) if you have exposed your ip address by posting to this board, but if it were me, and I was like you again in control of my bitcoins, I would move them to an address which was not found in any of the old backups which use the weak password, this might require sending them to your online wallet. Then I would generate a new wallet in Bitcoin-Qt, this time with a secure password/passphrase and then make a backup of this new wallet (being careful to distinguish it from the old wallet) and send your bitcoins to this new, more secure wallet.
If you are the nervous type, or want to be extra safe, I often send test amounts when setting up new wallets, just to make sure there are no password problems or whatever. Probably best this tim ein any case, as you have stated that it is 90% of your net worth, to use a test amount first at all steps.
i would do this because I would be worried that someone could find/steal an old backup you have on your computer, knowing that it has an 8 character password (dramatically reducing the keyspace to search in) and take your coins. Sending them to a new address generated by Bitcoin-Qt using your existing wallet will only be sending them to one of the 50 pre-generated recieved addresses stored (hidden) in each backup, this is why I would advise a new wallet file altogether.
I would also be tempted to follow willphase's advice about being extremely careful doing this kind of thing, and ask for help if you need it. Also candoo has wise words about storing bitcoins in paper wallet, for better security. There are guides on how this should be done if this is the route you want to go down.
If you have a smartphone, I would advise you to buy a password manager app, I use 1Password (for iOS). This app is secured using a 50+ character passphrase, generated using words from
this site, this is the only password I have to remember any more. I did not use a pre-generated passphrase from this site, but instead used some of the words it gave me to form a sentence of gobblede-gook (important:do not use song-lyric, movie phrase etc, it must be random!)
This lets me use random alpha-numeric-symbolic passwords of any length for all websites as required, using a unique one for every site I visit (bar some ones I dont care about where I re-use a simple password). For encryption purposes, length is the important factor, so passphrases (like the type found on that formilab site) do a good job. For bitcoin wallets, USE 12 CHARACTERS OR MORE. No dictionary words. No clever subsitutions (i.e. 1=i, 3=E, S=$). No common phrases, song titles/lyrics,movie lines, anything which you already know. Also, humans are terrible at being random, thats why i use that
Formilab site to get me started, then I randomise that.
My 1Password app is setup with auto-encypted-backups to my dropbox every time I change anything, and it also save all previously used passwords in the backup file, which is neat.
Sorry that I veered slightly offtopic there... You know what they say, 'better safe than sorry'!
Ontopic, I will try to reproduce this error when I get home tonight
