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.

If you want, you can just open Bitcoin Core, go to Help>Debug Window>Console and use

Code:

dumpprivkey "Address"

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)

btcdeep