Coded step fails to complile even after assembly reference added

I am trying to add a coded step where I can write data to an Excel file.
I have added the reference in Project Settings -> Script Options -> Add reference from the location below:
C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v3.5\Profile\Client

However, when I run the test, it still fails to complile my coded step. View log displays the error as follow:

c:\Users\Nhan Ai\Documents\Test Studio Projects\Beats Automated Tests\WebTest.tstest.cs: Line 86: (CS0234) The type or namespace name 'Office' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?)

And in the code Viewer, these line are highlighted.

Microsoft.Office.Interop.Excel.Application excelApp = new Microsoft.Office.Interop.Excel.Application();
Microsoft.Office.Interop.Excel.Workbook workbook = excelApp.Workbooks.Open(myPath);

Please help!
Thank you,

Nhan Ai