crash on startup with the words error in assign id cannot find zythum category 0

Are you by any chance using the "Item Collectors" or "ZRecycling" mod?
I found that I did not sort those properly before release of version 1.0.0, sorry about that, they will definitely be fixed in an update later today though.

If you are not using either of those mods, could you please provide me with a list of mods you ran along with zythum, that will help me track down the issue.

no i was using both of those mods actually... i just added a boatload of mods the other day and that was one of them... so that was the reason it crashed then?

Most likely yes. I accidentally added those two mods to 1.0.0 without properly sorting them, which caused the mod to crash on startup.

I improved the build process of the mod a bit, so this shouldn't happen anymore in the future. You can download the current 1.0.1, that should fix the problem. Although ZRecycling is not yet sorted with that version. I'm still working on sorting more mods.