Question about PK2

Hi RZ,
is someone here who has good knowledge about pk2 ?
I thought about make new Sort of Item.
But when i add it in item_group.txt and reference in my itemdata_xxxx.txt to that group it always crashes.
Do someone know what i am doing wrong ?
I also add everything in textdata_object.txt
Do i need to create a item group on db site too ?
i didn't found anything there.
Please help.