solidworks tooling split cannot knit sheet together

I always have this problem when trying to do tooling split in solidworks ,
after having parting line , shut off surface and split surface when do tooling split it says cannot knit surface ,
i think it is about parting surface
so i have tried both creating parting surface through mold tools and manual surface with shut-off trim (i found on youtube)
but the problem continues .
i'm sure that i don't under stand it completely.
3 Answers

i have modified the split surface location it did create split tools but the core and cavity have no curves of the part