Did you perhaps only import the "address"... and not the "private key" for address DfbVmexCDLhbsSEGEjSXPAQXGhE7ECKghb ?
On the main preview window, do you see "watch only" balances listed next to the "spendable" balances? Do you see the "eye" symbol next to transactions in your transaction history that involve that address? If so, there is a good chance that this address is a watching only address and your wallet simply does not contain the private key for it... ergo "Private key for address DfbVmexCDLhbsSEGEjSXPAQXGhE7ECKghb is not known (code -4)"
let's start at the beginning :
I installed the wallet
That wallet has an address in it
when trying to run the command dumpprivkey, followed by that address, it's not giving me a private key for it.
Error : Private key for address DfbVmexCDLhbsSEGEjSXPAQXGhE7ECKghb is not known (code -4)
So , I assume that a wallet with only one address in it should have a private key for that address, no?
On the main window I have :
Spendable : xxx amount
Stake : 0 amount
unconfirmed : 0 amount
Where in the transaction list should I see this "eye" symbol, because I can only see (on the left) a circle that is checked.. for all of those transactions.