Problem with variable substitution

Hi specialists!

I try to take file name from one of the payload fields. But it didn't work.

Here is my message:

<InputMT>

<Message>

<data1> </data1>

<data1> </data1>

<data1> </data1>

<FileName> </FileName>

</Message>

<Row>

.

.

.

</Row>

<Line>

.

.

.

</Line>

</InputMT>

Here is my variable substitution:

var1 payload:ImportOrderFileMT,1,FileName,1

My File Name Scheme in CC:

ERRBED120%var1%.txt

The error is:

The following variable was not found in the message payload: var1

What's wrong?