If you have imported a part and are trying to convert it to a sheet metal part and it is failing, one possibility is the bend faces are spline surfaces. You can test this by trying to apply a Radial SmartDimension to the face, if it fails you know you have spline faces. A trick to work-around this problem is to export the part out to STEP AP214 then import it back in again. That should convert the spline faces into cylinders and allow for the conversion to a sheet metal part.