"Error saving the image. Check file extension" message when saving a captured frame with VC3Viewer, using a Watchport/V2 or Watchport/V3 USB camera

This message doesn't necessarily mean that the file extension is invalid. It may be due to the location where the file is trying to be saved, i.e. the Windows user account may not have permissions to that folder. Try saving the file to other folders, i.e. the root c:\ folder for troubleshooting purposes, initially, then other folders that have appropriate permissions.