While I was still in school, I connected with a professor who connected me with a buddy of his who was working at a large insurance company and doing some of their internal learning course development. He had developed some software that enabled people to author courses in Microsoft Word, and export them with the click of a button so they would be saved as Scorm packages. Scorm is a spec that lets you take your content with you from LMS to LMS. It was an awesome setup, and my job was to make sure that a system like Moodle would work with his packages that would get exported. I worked with a couple different LMS systems, both in PHP, and hacked them to make sure they'd work with some of the magic that his software did. We got a proof of concept, and even got a basic course online. I think it was a sexual harassment training or something along those lines.
And then it sat there. We had no plan for sales, no plan for marketing. I was still in school, and had no idea what sales/marketing for this should have looked like. My business partner was an HR guy, and was pretty happy at his job, so probably wasn't going to leave it and strike out on his own without something already rolling. We had no money, no plan for pitching investors, or anything along those lines.
So it died.
Problems with this venture:
Wasn't really thought through how we were going to do sales and marketing
Not sure we really hit the head of a really difficult problem for corporations
No real technical advantage (Scorm by definition is a spec so it should be apples to apples)
One of my first blatantly obviously failures that just wasn't thought through very well.