Facebook is reporting another data error, and it's giving some advertisers their money back

Facebook has found another data error related to advertising, and this time it has to return some cash to marketers.

The social network giant recently discovered a data bug tied to a specific ad unit known as video carousel ads. These ad units allow marketers to showcase multiple ads in a single ad slot in Facebook's news feed.

In some cases, when people clicked on one of these ads to watch an advertiser's video, Facebook was reporting that people were actually clicking all the way to that advertiser's website or app.

Unlike several of Facebook's more recent measurement errors, such as providing inaccurate data on how much time people were spending with video ads on Facebook, this carousel mishap was fairly limited in scope. It only oc cured when people accessed Facebook via a mobile browser like Safari or Chrome, and not via Facebook's mobile app or desktop site. And it only impacted a few advertisers.

Still, the bug went undiscovered for roughly a year, meaning that some advertisers were paying for clicks they believed would potentially result in visitors to their properties for an extended period of time. Thus, Facebook is sending these advertisers refunds.

Overall, the company expects that it may have impacted 0.04% of ad impressions during that period. That's hardly going to impact Facebook's revenue trajectory, but given the growing volume of ad-related metrics mistakes, it's not what the company needs right now.

Advertisers have long complained about the perception that Facebook and Google don't allow for third party measurement companies to the same degree that most media companies do (such as TV networks having their ratings tracked by Nielsen). This mobile rebate will only add fuel to that fire.