SSRS 2008 “Unknown Collection Member” Error

This is driving me nuts. I added a column to a DataSet in my SSRS Report. I refreshed the fields and now the column displays in SSRS.

I want to place the value of this in a TextBox.

1. I added TextBox to the report
2. I right click the TextBox and pick "Expression"
3. In the dialog box I click Datasets –> MyDataSet –> First(MyNewColumn)

The results in the expression in the SSRS TextBox being

=First(Fields!MyNewColumnName.Value, "MyDataSet")

I then get a red squiggly line and an error that says "Unknown Collection Member". This is a lie, because it is part of the collection. I have verified that this value is returned when I run my query in SQL2008. When I preview the report I get "#Error"

Does anyone know what the real problem is here?