'FirstComponent' could not be found

Hi, how can i get directly the field of a table row in a numerical component?

I get the row with an "invoke data source method" and store the result a property, perfect works
Then on the numerical component i want to use as value ${SelectedItem.heattransfer}.

But the i get the error: The Type or namespace name 'FirstComponent' could not be found.

Also tried: ${SelectedItem.heattransfer.Value}.
or ${(int)SelectedItem.heattransfer.Value}.

Both with the same result.

We are not sure what SelectedItem is. Also what is FirstComponent? Can you clarify?