Category Drag-n-drop

[Aubrey]

I want to move a category but I am unable to drag and drop. (see attached jpg).
I'm trying to make "Lake McIllwaine" a child of "Harare"
I've performed a database diagnostics all is OK.
What am I doing wrong?

Aubrey.

[Aubrey]

Update:
Solved.

Rebooted PC and it works ok.
bizarre?

Thanks