Palette items not dragging

I understand that there have been others on this site who have experienced the same problem, but unfortunately I haven't been able to find any suitable or helpful answers to it.
The problem is, I was just working on a score and I was about to drag on a time signature change from the palette bar, and it wouldn't drag - as in, the item wouldn't follow my cursor to the place I was dragging it. It is not that I was doing anything wrong, as it was working mere minutes earlier on the same score, but I'm assuming it has something to do with the program. I have tried exiting and reopening the same score, opening a different score instead, and restarting my computer, but none of them have made a difference.
This has become incredibly inconvenient, because although some items from the palettes can be imported simply by clicking on the wanted bar/note and then double-clicking on the item from the palette, others are not - for example, I'm pretty sure the page/line breaks need to be dragged on in order to function.
The same thing is happening for all items in all the palettes - I cannot drag any of them onto the score. And, in case you were wondering, the same thing is happening for the master palette (Shift+F9).

If someone can explain how to fix this, I will be extremely grateful. Does it fix itself, or is there a manual setting I need to edit? Thanks in advance!