Blockmarket 1.2.3 will not sync because it connects to the 2.0 chain which is no longer running. Syncing to the 2.0 chain is not necessary - all you need is to dumpwallet.
In Blockmarket 1.2.3 go to the console and use the dumpwallet command:
In Windows use this location(with no quotes):
(xxxxx is your username)
Then you should be able to find the file in that folder, then import that into Blockmarket 3.0