Error using Matchfrequency stage in qualitystage job

[shaonli]

Hi,

In my job after using standardize stage (USNAME rule set) I want to use match frequency stage.So after standardize stage I am using a transformer(according to Quality stage tutorial) where I am creating a column named MatchFirst1(Varchar1,Nullability yes).
The derivation of this field is
If isNull(Standardize.MatchFirstName_USNAME) then Setnull() Else Standardize.MatchFirstName_NAME[1,1]

Then this column along with other original i/p columns(Name,Addr) is input to the Match frequency stage.The o/p is fine.

But if I don't derive the column MatchFirst1 and input the original fields only to the match frequency stage then the error comes "MatchFirst1 not found".
Can you please explain why this column is required?

In the derivation of that field instead of MatchFirstName_USNAME column if I use any other column of rule set o/p(eg:AdditionalName_USNAME) then also it is working fine.

What is the significance of creating this column.Please give your thoughts
.
Thanks in advance
Shaonli