When I try to load my Bitcoin Wallet I get an "Assertion Failed!" window: here is what the window says:

Program: C:\Program Files\Bitcoin\bitcoin-qt.exe File: src/main.cpp Line: 1761

Expression: pfork !=NULL

For information on how your program can cause an assertion failure, see the visual C++ documentation on asserts

(Press Retry to debug the application - JIT must be enabled)

(three buttons:) Abort Retry Ignore

I am a novice and don't know where to start. I do have a backup on a flash-drive if that is of any help.

Many, many thanks for any help you can give. Sincerely Douglas (Scotland, UK)

  • Which version of Bitcoin-Qt? Aug 28, 2013 at 20:48
  • Version: bitcoin-0.8.3-win32 - Windows XP. By the way, it loads quite happily under another username on the same computer. By the way, I have uninstalled and reinstalled to no effect. Many thanks for your help
    – user6542
    Aug 29, 2013 at 15:10
  • Did you initially install it under the user account where it works or where it does not work? You may have to reference a data directory when you open it, see bitcoin.stackexchange.com/questions/6015/… Aug 29, 2013 at 19:54
  • 4
    bitcoin-qt bugs are best reported on their issuer tracker at github.com/bitcoin/bitcoin/issues
    – dchapes
    Aug 30, 2013 at 14:16

2 Answers 2


Found out a way to fix the problem - really easy too:

1) Copy bitcoin data files to external hard drive 2) Uninstall Bitcoin application 3) Copy bitcoin data files back to their original location 4) Download and reinstall Bitcoin application. It finds the old files and everything works perfectly.

Thank you all for your help. D


The only thing you need keep between installations of bitcoin is the wallet.dat file, which contains the keys required to spend your coins. If you are reinstalling bitcoin you can use bootstrap.dat in versions after 0.7.1 (at the time of writing the current stable version is 0.8.6).

Here's how to use bootstrap.dat to avoid the painfully long block chain download for a new installation: https://bitcointalk.org/index.php?topic=145386.0

Even if you've already downloaded some blocks, bitcoin will check for bootstrap.dat and sync. At the time of writing the file is 13+ gb, but you can delete it once that your client has verified all the blocks.

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