There was a lot of False Solomon's Seal (Maianthemum racemosum) growing among the saskatoon berries. When picking the low Saskatoon berries it could potentially be easy to accidentally pick a False Solomon's Seal. The berries look similar at this time of year on quick glance. So I did some quick online and book searching to check if it is poisonous (as I may take the kids next time). My book source  does not indicate edibility, but a few online sources indicated they are "edible, but no palatable" and high in Vitamin C , .
Also, "the fruit is said to be laxative in large quantities when eaten raw, especially if one is not used to eating it, though thorough cooking removes this laxative effect. Young leaves are edible, raw or cooked. The young shoots, as they emerge in spring, can be used as an asparagus substitute. The young shoots and leaves are cooked and used as greens. The root is edible cooked. It should be soaked in alkaline water first to get rid of a disagreeable taste. It can be eaten like potatoes." Medicinal uses are also listed at the link.
So it appears the occasional False Solomon's Seal berry will not do much harm if not too many are eaten at once.
 Wildflowers Across the Prairies, Field-Use Edition, F.R. Vance, J.R. Jowsey, J.S. McLean, Western Producer Prairie Books, Saskatoon, Saskatchewan, 1977.
 Montana Plant Life , accessed August 7, 2011.