I suspect the issue will be because I dont have an optional depends for that mod. If you add bakedclay to the comboblock mod.conf it should work so copy and replace the text in the current mod.conf in comboblock with the below. I'll add this in when I do the review to make sure it's working for MT 5.6, I'm very behind on everything.
name = comboblock
description = Allows the stacking of slabs vertically
depends = stairs
optional_depends = farming, cracked_castle, moreblocks, jonez, bakedclay