I have been having some difficulties ever since switching to 2018 (so far i do not view it as an upgrade)

todays issue is regarding a "failure due to geometric conditions"

I have attached the model and the slot with which i am trying to split the part - or cut extrude - or surface extrude the slot and cut with that.

all fails

can anyone suggest why this is not working ?

Need to split the part both directions with the drawn slot

Thanks
Brant