AutoCad :: Cannot Change Any Object Layer Association

for no apparent reason I am suddenly unable to change the layer that a object is assigned to. Normally I select a line, then go to the layers pull down menu and click on the desired new layer. Automatically the line changes color to the selected layer.

When I follow this procedure now, the layer name changes in the pull down menu as if the change has been made, but the line remains the old color. Checking in Properties for this line, it shows that it has been changed to the new layer as well, however, when I reselect the line, the Properties changes back to show that it is still assigned to the old layer (color: By Layer is selected).