ABC News' Eloise Harper Reports: Senator Hillary Clinton's campaign has held multiple fundraisers over the course of the year featuring high-profile singing groups including the Goo-Goo Dolls and Elvis Costello.So, when Elton John agreed to host a "one-night only" concert for the Senator, one would think it would be a sold out event. Campaign aides assure ABC News that orchestra and mezzanine tickets sold out in an hour after they put the tickets online, and only a limited amount of tickets are still available. But since the initial announcement, the Clinton camp has sent out at least eight nine reminders about the concert, raising some question as to just how available the hottest ticket in town might be.On March 17th, Hillary Clinton supporters and donors got an email in their inboxes that said "I'm Throwing a Party." It was from Elton John. The campaign also sent out a text message announcing tickets were on sale. That same day the campaign sent out two emails to reporters announcing the concert. On March 20th in the Morning "Hubdate" -- a daily note sent to reporters -- one of the announcements read, "Rocket Man Lends Star Power: Elton John will headline a major fundraiser for Hillary in New York on April 9th."Five days later, Hillary Clinton wrote an email to donors and reporters, with the subject "You, Me and Elton John," encouraging supporters attend a contest for the show. Chelsea Clinton then followed up on March 26th with a personal email inviting guests saying, "My mom's campaign is bringing two supporters and their guests to New York on April 9 for both Elton John's one-night-only concert and the party after the concert. It's going to be a great night and a great time."That same day came a text message from Hillary Clintons campaign's campaign for a contest to win tickets to the concert."Want to see Hillary and Elton John on April 9th? You could win tickets to the 1 night only concert. Enter at HillaryClinton.com."The campaign tells ABC News that this is standard protocol for high profile events. One aide said, "It's a huge deal," and asked why they wouldn't want to do everything thing they could to promote the concert.