Solution for ; error: bad argument type: VLA-OBJECT nil

I run into a problem in AutoCAD trying to get a VLA-OBJECT property like this with AutoLISP/ActiveX:

(vla-get-linetypes (vla-get-activedocument (vlax-get-acad-object)))

The error:

; error: bad argument type: VLA-OBJECT nil

Accessing other properties also failed.

Reinstall of AutoCAD was needed to solve the problem. Repair did not help.