Processing of the LINQ expression 'GroupByShaperExpression

[TonyValenti]

This Code:

            var MatterTrustBalances = (
                from x in MatterTrust.GroupBy(x => x.Dest_Matter)
                let v = x.Select(x => x.Dest_Amount).Sum()
                select new {
                    Matter = x.Key,
                    Balance = Math.Max(0m, v)
                }).ToDictionary(x => x.Matter, x => x.Balance);

Generates this error:

System.InvalidOperationException: 'Processing of the LINQ expression 'GroupByShaperExpression:
KeySelector: _.Dest_Matter, 
ElementSelector:EntityShaperExpression: 
    EntityType: MatterTrustBalanceImportJob
    ValueBufferExpression: 
        ProjectionBindingExpression: EmptyProjectionMember
    IsNullable: False
' by 'RelationalProjectionBindingExpressionVisitor' failed. This may indicate either a bug or a limitation in Entity Framework. See https://go.microsoft.com/fwlink/?linkid=2101433 for more detailed information.'