I suspect it's a made-up word referring to broadcasting a show over the internet, similar to webcast or podcast. "The showcast could not be played," sounds like an error message.

If a group of people perform a "show", they are referred to as "the cast". Cast and crew is a common reference. The crew being the stage assistants, and so forth. They manage the lighting, costumes, and any other material needs. "Showcast" is a bit awkward. Cast is more common. It would be common to see a wording like this; "The show could not be played." "Cast" would not be included in such a phrasing.