xTray-2.0 (as well as the other xModules (2.x, 4.x) and other newer modules) need xPaintClass-1.0. But the displayed error message should have stated this already.

Solutions:
In the *NetLoadModule section i added:

*NetLoadModule xpaintclass-1.0
*NetLoadModule tasks-0.92-b3
*NetLoadModule Shortcut2-2.0

or

Download "xPaintClass-1.0 Update 4" at http://www.ls-universe.info and copy it into your Litestep root folder next to litestep.exe.