Problem : Invalid Geometry and invalid assignmentInvalid Geometry and Invalid Assignment

Hello, I am a new Ansys User, and in a Workbench Project i have to simulate a pin-on-bearing wear : i created the geometry of both parts (Pin and Bearing) in NX 11.0 and exported the file .STEP to Ansys to simulate it. The meshing works perfectly, but when i click on solve button, i get an error message showing (Invalid "geometry"). i was first using Ansys R15 then changed to the version R19. Please tell me what i am doing wrong ? Thanks.