Select face and add sketch

Hi together,

i created a UI Block Designer where i can select a face the ID will be face_select0.

I try to find the face with:

< NXOpen.Face face1 = (NXOpen.Face)workPart.FindObject("face_select0"); >

But this does not work. I get the error " No obect with this name found in NXOpen.NXObject.FindObject(String journalIdentifier)

Where is my problem?

Afterwards i want to add a sketch on this selected face. Maybe anybody can tell me what should be the first step!

Best regards!