Seems you have the Windows Wallet. Just get the Addresses from the Addresses Tab in the Wallet. Then proceed with the other steps.
Actually I tried that, every single address =
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14:15:43

Private key for address 8N8ySmaNMeqLsEdzBzigVHMfBaf4xS8vTr is not known (code -4)
14:15:59

dumpprivkey 8ePeoUrCBzJLsnfiM2azy9rzRkCgHDohPq
14:15:59

Private key for address 8ePeoUrCBzJLsnfiM2azy9rzRkCgHDohPq is not known (code -4)
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