other pages as well.

eg.
Schlegal has a post pinned of his classical lessons...
and those links worked for a while...

but then every one I clicked on gave a [this page doesn't exist]

I brought that to Schlegal's attention; and if I recall he told me [GT changed something in their database at some point]; or something to that effect.

in general...

periodically I'll come across a link in a blog post; that results in said error
but I have no idea if those are links to another blog post; or lesson set; because the link is broken.