I had an offline/online-watching-only wallet of version 1.9.8. Recently i tryed to spend some of my BTC and got a "your wallet created a transaction which is no longer accepted by bitcoin network, you need to upgrade to 2.5.x" or something like that message. Since I didn't want to upgrade, I tryed to broadcast my transaction via blockchain.info, but it also told me that my signature is non-canonical.
So I decided to upgrade. The watching only part of the wallet was upgraded without problems. I see all my addresses with their respective balances. Since the offline part of the wallet is not supposed to ever be connected to any networks, I downloaded the sources distribution, unpacked it on the offline computer, launched. But I cannot sign my transaction. There is just no 'sign' button. Fortunately I see some of my addresses, so I suppose the master private key is intact. Where it is stored btw on a Linux machine? But the address from which I want to spend isn't among the first several addresses, so I suspect, that my offline client just doesn't know that it has private key for that address. Am I right?
And another thing looks weird. While the first 4 receive addresses coincide in online and offline clients, the 5'th address differs. I don't see the 5'th address from the offline client in the list of receive addresses in the online client nor I see it among change addresses. All 6 change addresses that I see in the offline client coincide with the first 6 change addresses in the online client.

Please help.

P.S. The online client runs on Windows.
And I've found out where Electrum stores wallet files. I'm not an experienced Linux user, being accustomed to Midnight Commander I didn't know that ls without arguments doesn't show those special folders whose names begin with '.'.