ok ,this was my problem ,In older version of OpenBSD(like 3.9) I must do small letter "d" and then letter "a",but in new version I don't must do this ,only I must create slice with "a a",I didnt' know about this
In FAQ there is version that I should do "d a" to delete partition and make slice ,but in newer version of OpenBSD I can't do this becouse I had communicate"Partition a is not in use",ok thanks for your help
It's working
I installed new 4.3 OpenBSD