Doesn't work perfectly for subplots but...
I managed to get it to work reasonably well (on 1 occasion with an Area subplot) by...:
1) - Open gridLegend .m file and comment/delete line 273.
2) - If you are getting errors about Scribelegend, delete lines 278-284
3) - Specify a location (I used 'location','southoutside' )
Basically the issue with subplots (from what I can see) is that gridLegend is trying to control the 'gca' which doesn't seem to exist in subplots.