Documents seen by RTÉ News show that the US Secret Service confused Sinn Féin leader Gerry Adams’ name, as the nickname of another guest attending an event at the White House last year.
Mr Adams was refused entry to last year's St Patrick's Day event at the White House.
A member of the Secret Service did not see an email about the problem because they had gone for a run and another official described the whole affair as a "firestorm".
Last year, there was a delay processing Mr Adams' security clearance as he tried to attend the traditional St Patrick's event hosted by former US president Barack Obama.
Mr Adams left after waiting for more than an hour.
Documents released to RTÉ News under Freedom of Information show that the delay happened because the Secret Service thought "Gerry Adams" was a nickname for another guest attending the same event.
When an email was sent from a member of the Secret Service to a colleague informing them that Gerry Adams got tired of waiting and left, the reply is: "Ha. Sorry, went for a run. Had to get out in this good weather."
In a follow up email, the person writes: "Yesterday I went for a run at 5pm and did not get back until 5.45pm when I saw the email."
The issue generated a lot of emails between the Secret Service and the White House, with references to negative press coverage and a letter signed by members of Congress.
One Secret Service official writes: "I walked into a firestorm... the last flames are just being put out as we speak. Wow, what a day!"
Another Secret Service email says that Mr Adams is "being very vocal about this and has gone to the press saying he was denied entry which we obviously know isn't true."
Today, a Sinn Féin spokesperson said last year's incident was regrettable, adding that Sinn Féin was given a different explanation at the time.
The statement does acknowledge however that both the White House and the Secret Service have aplogised.