SSIS: “Error: The result of the expression ”@[User

Question

I have been trying for the last 10 hours to solve the following problem:

I have a ForEach Loop container that is enumerating Excel file names in my Control Flow. Within the ForEach Loop container I have an Excel Source that imports data into Sql-Server. This connects to a Derived Column transformation using User::FileName as the expression that connects to a OLE DB Command that that maps to the User::FileName to a Report_Date (the Excel file names contain the report date) column in Sql-Server to the relevant rows.

The following is a snip of my Control Flow:

I keep getting the following exception:

Error: The result of the expression "@[User::FileName]" on property "\Package\Foreach Loop Container 1\Data Flow Task.Properties[[Derived Column].[Derived Column Output].[Derived Column 2].[FriendlyExpression]]" cannot be written to the property. The expression was evaluated, but cannot be set on the property.

Ive tried everything I know and can't get rid of it. Running out of options.

Am I missing a step in the process?