The focus control is not available for the selected camera
This VB example uses the minimum and maximum focus values to initialize the slider control:
Private SubForm_Load() Slider1.Min = ActiveDcam1.GetFocusMin
Slider1.Max = ActiveDcam1.GetFocusMax
Slider1.Value = ActiveDcam1.Focus
If the currently selected camera doesn't support software focus control, the method will generate an error.