Rhino View Port Shows Nothing

Hello all;

Occasionally, my rhino view port will suddenly display nothing in the active view window. I can not see rhino objects or grasshopper objects.

This tends to happen when "Perspective" view is active, but not always.

I can use Ctrl+A to select all, but when I type ZoomSelected, it returns:

"Unable to Zoom - on objects are selected""

I have seen this error happen on a few computers. It is hard to recreate, but it seems to happen when I have a python script in the definition. 

import rhinoscriptsyntax as rs

if activate == True:
    Camera = rs.ViewCamera()
    Lens = rs.ViewCameraLens()
    Plane = rs.ViewCameraPlane()
    Target = rs.ViewCameraTarget()
    Up = rs.ViewCameraUp()

This output the current information about the active view port. Not sure if this is the cause. I am also using this information to make custom previews and 3D text tags that float on the active view port window.

If anyone has an idea of how to avoid this problem, I am all ears. I have made a python tool to fix the problem, but I would like to know the cause. 

Thank you in advance for the help!

Kind regards,

Jake