Sometimes when the Bitcoin-Qt client has the wallet open there are crucial pieces of data held in logfiles.  When the client shuts down, that process properly closes the wallet.dat and the file has data integrity.   If the client crashes or has some problem shutting down, the wallet won't have been closed properly.  Normally when that happens the client can be restarted and the data from the log files will be used to recover (rollback) the wallet or clean up, with not even a hiccup noticed by the user.  If you grabbed a copy of the wallet.dat while it was not in a closed state or was in need of recovery, then now when it tries to perform that recovery the needed log data is not accessible.

That may be what happened, or perhaps there was a media error with the backup, or the wallet.dat was already corrupt but the client didn't notice (the more recent releases are more stringent about checking validity) or any number of explanations for why currently the wallet.dat is unreadable.

What you can do is try to salvage the wallet.

Run Bitcoin-Qt manually from the command line and do a -salvagewallet

That moves the bad wallet.dat to wallet.timestamp.bak, then runs a 'salvage' operation to get key/value pairs, and writes them to a new wallet.dat.  Then the client continues from there.  If there was keys in corrupted data that it couldn't recover, those won't be in the new replacement wallet, but if it was able to salvage everything you won't be missing anything.

Thanks for the quick response.  I have tried that on my "new" windows QT client, and the QT just quits out.  No error, but no progress.

So I decided to install a new Ubuntu VM, to see maybe its a Linux/Windows compatibility issue, or if maybe the salvage only works on Linux.

Running the -salvagewallet argument has the same result on my new linux QT client as well.  ie, the client quickly loads and closes without a peep.  It does not appear to attempt creating a backup wallet file that I can see.

I would appreciate any more ideas you or anyone else may have.

I've gotten to a point where I can run pywallet on a new unencrypted wallet.dat file.  But when I try to run it on my backed-up, encrypted file, it doesnt work.  Have tried the "--password" option that I saw somewhere but that appears not to be an option.

Any help recovering keys/fixing an encrypted wallet using pywallet?

Thanks.  I am now using the joric pywallet.

I've got two problems.  Both of these problems occur on both the jackjack and joric wallet:
1) I am getting an error when running it:  "ERROR:root:Couldn't open wallet.dat/main. Try quitting Bitcoin and running this again."
2) When I try to use the "--password" option, I am getting an error, I think because I have an exclamation point in my password.  I realize the jackjack pywallet doesnt accept the password option, but this also happens on the joric one.  Is there a linux switch (i've tried using \'s) that would allow the syntax?  I am fearful even if I get over this step, I'll be stuck on #1.  An example of this error (assuming my password is "ab!c" is below.  Any guidance please?

=========

If pywallet can't read it and salvage wallet can't even load it ... that's not good.  You don't have any older backups?  If you had backup media (e.g., flash drive) have you re-tried re-copying from the media with both pywallet and then -salvagewallet  (i.e, not used the same wallet.dat after one failed and then trying the next?)

The last ditch approach might have worked except that it only works for non-encrypted backups:
 - http://bitcointalk.org/index.php?topic=25091.0

But the number one lesson about backups ... if your backup can't be used to recover the database, then you have no backup.

Thanks so much for the continued help.  Here is where I am at now:

A) I've been storing my wallet backups as an embedded object in Microsoft Excel.  I've determined that this does not work.  I've tested this - I take a wallet that can be pywallet'd, embed it as an object in Excel, then copy it out of Excel, and suddenly pywallet complains.  Anyone have an idea how to circumvent this - this would by far be the easiest solution!
B) Trying to recover my Virtualbox VDI drive.  This is a long shot

Clearly I screwed up assuming backing it up in a spreadsheet (that gets backed up automaritally daily).  Lesson learned.

Any ideas?

\O/ 

+1 for multiple backups using multiple media (e.g., one kept locally like on a flash drive, and one backed up online somewhere like Dropbox (perhaps encrypted using TrueCrypt, even with Bitcoin-Qt's passsphrase encryption)

Salvage doesn't work too well right now, most cases that cause you to need to salvage make the salvage 'fail' (it fails whenever the database layer returns an error). If the wallet is not encrypted I usually recommend people to just use the private key recovery tool: https://bitcointalk.org/index.php?topic=25091.0   if you need to recover an encrypted one, I can give you a patch to make the salvage more robust.