YouTube blocked educational videos from MIT and the Blender Foundation.

There was speculation that YouTube's content-filtering system is to blame but YouTube says the problem is administrative in nature.

Regardless of the causes, the incident highlights the world's increasing reliance on YouTube as a video distribution pipeline that goes beyond entertainment, and YouTube's challenges handling that responsibility.

Late last week, videos from MIT OpenCourseWare posted to YouTube mysteriously became inaccessible on the Google-owned site.

OpenCourseWare is in charge of sharing teachings from MIT, one of the country’s most respected research universities, with the rest of the world. The school’s most popular videos on YouTube are typically recordings of lectures on computer science and mathematics. It's not the kind of thing that might be considered unsavory, controversial or a violation of YouTube's policies.

And yet, YouTube decided to block these educational videos from public view. The school wasn't informed of the reasons and hasn't a clue about how to get them back up. As of Tuesday afternoon, the videos were still inaccessible.

“We’re quite frustrated by it,” said Curt Newton, the MIT OpenCourseWare’s director, in an interview Tuesday with Business Insider.

He said the program’s YouTube videos generate millions of views from across the globe. Teachers use them in their classrooms. Students study them.

Also late last week, the same thing happened to clips from the Blender Foundation, the nonprofit that oversees the Blender open-source 3D content-creation program, according to a Blender blog post.

YouTube hasn't said much about why the videos were blocked to the site operators or journalists.

A lesson about our dependence on YouTube

“Videos on a limited number of sites have been blocked as we updated our partner agreements,” the company told Business Insider in a statement. “We are working with MIT OpenCourseWare and Blender Foundation to get their videos back online.”

The only problem with that is MIT and Blender say they’re completely in the dark as to why their videos were blocked or when they might return.

The leading theory among tech-news sites is that the cause of the trouble must be a glitch with YouTube’s content filtering system. The filter is supposed to scan videos and flag those that violate the site’s policies. In practice, disturbing and graphic video clips sometimes get through the filter while benign videos that adhere to YouTube’s rules are removed.

YouTube’s statement that the problem lies with the company’s partner agreements seems to indicate that the problem might simply be an administrative, paperwork issue.

Whatever the reason, the incident shows our dependence on YouTube as a fundamental part of a modern infrastructure, in which entities from news publishers to universities depend on it to distribute videos.

In the past few years YouTube has appeared to struggle to maintain control of a site that sees more than 400 hours of video posted to it every minute and 1.8 billion viewers every month. All that growth appears to have made YouTube enormously valuable.

But the flip side is that one of the nation’s premiere universities had its videos removed, wasn't informed of the reasons and was prevented from resolving the issue after four days.