Trouble dragging menu bars in custom menu

I successfully created a custom menu and initially was able to drag & drop to create submenus of pages/categories, however now when I try to drag, the crosshairs act like a cursor and start highlighting the text on the menu bars, instead of moving them.

I have tried deactivating all plug-ins, same result. I switched browsers, same result. I created a new custom menu, same result.

Does anyone have a suggestion what coudl be wrong, or how I can fix this?

Thank you,
Ann-Marie