I think 0.8.3 is so old that it does not have the functions described such as abandon transaction. All I can do is view the transaction details (amount and addressee), or view transaction ID
I have checked with an old copy of 0.8.6 as I don't have 0.8.3... and it has the console available (Help -> Debug Window -> Console) and
dumpprivkey works as it should:
Note: the first address is not in the wallet so "code -4" is the correct response.
If you are getting the "Private key for address XXXX is not known (code -4)" error, then you are most likely using the wrong address with the command... Click on the "receive" tab and then try the
dumpprivkey command with one of the addresses shown there, to confirm that it is all working OK.
Figuring out which addresses in your wallet the bitcoins are actually on is going to be the next challenge... as they could be on change addresses, which I believe are not show on that "receive" tab. I'd probably be inclined to just use PyWallet to dump the contents of the entire wallet, extract ALL the private keys and then import them all into Electrum... and let it do the job of find which keys have coins
I am quite sure I have the right address applied because I only have one address and I have been using this wallet / address for years