DataGrid Footer Totals

Demo: orders.Sum(o => o.Freight)

I am using this footer total, and it works great, but it's throwing an "unhandled error has occurred Reload" when the page renders. If I replace my code below with a string like "test" then the error clears, so there's something about the code below it doesn't like. Any ideas? Thanks!

My code: bankerY.Sum(b=>b.YTDAmt)