Blockchain.info import wallet feature via wallet.dat no longer works, at least to my wallet and experience.
My experience is the same. two browsers on my regular PC, and IE on two other different PCs all same experience.
That feature was discontinued or hasn't been working for the past several months/years. I don't know why they still keep that page up though, confuses the hell out of everyone.
If you want, you can just open Bitcoin Core, go to Help>Debug Window>Console and use
to extract the private key. Import the private key to another SPV wallet. Make sure that the correct wallet.dat is in the data directory.
it gives error: Private key for address (myaddress) is not known (code -4)
Did you have a password on the wallet? If so, you must first run
walletpassphrase <passphrase> 120
where <passphrase> is your passphrase. This command will unlock the wallet for 120 seconds (2 minutes) in which time you must do all of your private key operations (dumpprivkey).
I also highly recommend that you continue to use Bitcoin Core. Install the latest Bitcoin Core from
https://bitcoin.org/en/download. Then put your wallet.dat file in the data directory. Then when you start Bitcoin Core, you may need to use the
-upgradewallet option, depending on what version of Bitcoin-qt you previously ran.