I didn't get any immediate suggestions so I completely removed Fences from my computer and reinstalled and that seems to have solved the problem. But I shouldn't have to uninstall to solve a problem. But it's fixed so I'm happy.
I have had Fences 2.12 on my one computer, 2 monitors, happily for a long time. Today I switched one of the monitors for my husband's old monitor. I had had 2 17" monitors, now have 1 17" and 1 27" (I know, looks weird). My problem now is that I have all the fences (5) on the small monitor and wanted to move them to the large monitor. I started moving one, dragged it and it stopped (wouldn't move left or right) half-way between the two monitors. I waited a moment and moved it back to