It sounds like you used artisteer-greenlagoon or artisteer-swirly1 as the starting point, those are for older Artisteer 2.3, all the newer skins intended as starting points for Artisteer 2.4 have artisteer-24 as part of the name. There is a difference between these skins in the theme.skin file which controls some aspects of the rendering such as the case of the css classes, in Artisteer 2.3 they were mixed case like art-Block-body (as in what you posted) but in 2.4 they are all lower case and since css classes are case sensitive the settings in the skins for 2.3 will not work in 2.4. So the problem is you used a 2.3 skin for a starting point instead of a 2.4 skin.
The instructions are clear about what skins to use for a starting point.
Hope it helps,