Adblock Plus, an adblocker with some 400 million downloads and counting, has been blocked from attending the Interactive Advertising Bureau's big annual conference. The IAB is the online advertising industry's main business organisation, and the conference is where all of the top dogs go to talk about the state of the industry.

According to a post on the Adblock Plus blog, the company had bought a ticket for the IAB conference, which takes place in Palm Desert, California at the end of January. The ticket was not cheap: they start at about £1,750 for members, scaling up to £2,600 for non-members.

Then, last week, Adblock Plus received an e-mail from the IAB stating: "We are returning your registration fee and cancelling your registration for the IAB Annual Leadership Meeting." That was the entire content of the communication; according to Adblock Plus, there was no reason given for the cancellation.

Adblock Plus employee Mark Addison e-mailed the IAB and asked if "there must be some confusion" as he hadn't asked for a cancellation or refund. All he got was another inscrutable email from the IAB, confirming that his ticket had indeed been cancelled, but offering up no reason for the cancellation.

In all likelihood, Adblock Plus was uninvited from the IAB event because they are, er, not exactly the best of friends. The IAB represents the companies that make money from online advertising, while Adblock Plus primarily exists to block online advertising.

Still, it's a little unusual for the IAB to just flat-out reject Adblock Plus. The IAB has previously acknowledged that adblocking is a huge problem for the industry, and the topic of adblocking was discussed at length at last year's annual conference. If a solution is to be found, it will almost certainly require a dialogue between the advertisers and the advertising blockers.

An IAB spokesperson declined to comment further on this story, instead pointing us to a very brief statement that it made last week: "The IAB Annual Leadership Meeting is for serious conversation among important digital industry stakeholders."