Create A Column Based On A Value In Created Column

I am trying to add a column to query based on the value of another column in the query.

I first tried creating a calculated field in SSRS 2008 with this statement:

=IIF(Fields!ChargeableFlag.Value=1,Fields!Negamt.Value,0)

The report runs but I get a "#ERROR" when I place the field on the report.

I next tried creating a new column with the SQL statement:

SELECT Project.ProjectCode AS PC, Project.StatusCode AS SC, Time.StandardHours AS Hours,
Time.StandardChargeAmt AS StdAmt, Time.TaskUID as UID,
Time.StandardChargeRate as Rate, ChargeableFlag, 'Bill' =

Case
When TaskRule.ChargeableFlag = 0 Then 'Non-Bill'
When TaskRule.ChargeableFlag = 1 Then 'Billable'

[Code] .....

This query, less the case statement for BLAmt creates the dataset for the SSRS. Adding the Case statement for the BLAmt produces the error: "Invalid column name 'Negamt'."