The Source

is Obama:

Barack Obama, the first African-American president of the Harvard Law Review, was born in Kenya and raised in Indonesia and Hawaii. The son of an American anthropologist and a Kenyan finance minister, he attended Columbia University and worked as a financial journalist and editor for Business International Corporation... His commitment to social and racial issues will be evident in his first book, Journeys in Black and White.

Thus reads  Obama's bio as published in 1991 by the literary agent who was hawking his book. That agent, of course, has taken ownership of the error:

"This was nothing more than a fact checking error by me--an agency assistant at the time," Goderich wrote in an emailed statement to Yahoo News.

But it does beg the question of the origin of the fact she failed to check*.  It is quite unlikely that an agency assistant would insert a birthplace, especially one outside the US, without checking with the author.  In fact, it is highly unlikely that she is the source of any of the facts in the bio. Agency assistants don't generally do independent research on people when the answers are a phone call away, and there is no way one can imagine this went to press without a final draft being presented to the author himself. The most likely person to have supplied those facts is therefore the person probably most responsible for the persistent rumors that the president was born overseas: Barack Obama himself.

But why would he do such a thing?  Because being born overseas makes him sound much more exotic than he actually is, and therefore more likely to sell his book. Sometimes, when all the conspiracies are exploded, the truth is too mundane to have been seen from the beginning.

* an error which persisted for a decade and a half, and is therefore not an error but a purposeful incorrect statement, known in the vernacular as a lie.