Didn't the Norse colony on Greenland fall to the Inuit in the late Middle Ages? I seem to remember the "Skraelings" invaded the island.
Besides the technical problems, there is simply NO HISTORY of it.
When we DO have history of Vikings traveling to Greenland and Wineland (America).
Although Snorri Sturlasson didn't record them bringing back any slaves, it seems likely, considering the Viking modus operandi in Europe, that they would have.
I've heard that theory but I've seen no evidence to support it. The consensus today seems to be the settlements declined as the Little Ice Age came on until the last residents evacuated.