You don't mention the radio, or if you're using SkyCat or Hamlib, but some radio's lock out the VFO when controlled by PC (FT-736R, early FT-847 for example) so the only option to scan the passband is mouse/keyboard in SkyRoof.
If your radio allows VFO when controlled with other software, there might be a problem with your radios settings (.json) file if you're using SkyCat.