Quarkcoin's bitcoin-qt fork won't recognise unspent transaction
https://bitcointalk.org/index.php?topic=231309.0 worked for me, as it says:


Export your private key in base58 format (how to do this depends on the software used to make the unconfirmed transaction, but I'm sure it is straight-forward)
Create an empty wallet in bitcoin-qt (can be done with renaming your current wallet.dat to wallet.dat.bak and launching bitcoin-qt. Just be sure to keep wallet.dat.bak...)
Launch bitcoin-qt
Import the private key into bitcoin-qt (see this: https://en.bitcoin.it/wiki/How_to_import_private_keys_v7%2B)
Quit bitcoin-qt
Run
bitcoin-qt -rescan
Wait
Wait...
Now you have the full balance of the single key you imported (compare with blockexplorer. If not, stop here and post in this thread)
Create the transaction you wanted to do without forgetting the fee
Delete the new, nearly empty wallet.dat (just rename it if you're not sure about that part)
Rename wallet.dat.bak (thus your original wallet) to wallet.dat
Done