if I then place the lid onto the top of the case and reboot, I get a disc error.

And the IDE cables are not being touched, in the slightest, at all, by the lid? Are you sure?

When you're getting intermittent failures like that, sometimes even the slightest nudge of an intermittent connection will make it work again. The slightest movement of any affected component will do it.

Also, check the IDE header for the solder problem. There is a photo of it linked in the other thread you posted on this topic.