Not sure if it makes a difference, but you checked for extra spaces due to copy/paste?
Otherwise recheck the key, privkey starts with a 5
I think that you must also use a label that is not already in use in your wallet, but not sure
Found it - the export drop-list had base 56 selected by default, instead of Bitcoin-QT

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By the way, is scan time really necessary? Perhaps next time it better to import with scan false?