SSRS expression throws #Error - any reasons?

Question

I am new to the SSRS This is expression i am trying but it's showing "#Error" i tried varies things but still not any progress any guess why might it's happening.

=IIF(Fields!MailMeans.Value = "M","METER",
  IIF(Fields!MailMeans.Value = "I","INDICIA",
    IIF(Fields!MailMeans.Value = "S","STAMPS",
        IIF(Fields!MailMeans.Value = "N","NO-MAIL","")
        )
    )
 )

Answer 1

Try using Switch rather than the nested IIF

=Switch(Fields!MailMeans.Value = "M", "METER", 
        Fields!MailMeans.Value = "I", "INDICIA", 
        Fields!MailMeans.Value = "S", "STAMPS")

Answer 2

This should also work:

=Switch(Fields!MailMeans.Value = "M", "METER", Fields!MailMeans.Value = "I", "INDICIA", Fields!MailMeans.Value = "S", "STAMPS", Fields!MailMeans.Value = "N", "NO-MAIL", Fields!MailMeans.Value <> "M" AND Fields!MailMeans.Value <> "I" AND Fields!MailMeans.Value <> "S" AND Fields!MailMeans.Value <> "N", "")