function substr in WebI

Hello Together,

System Information: BO 4.0 SP 2 Patch 10

I created a report with webi based on a SAP BEx query. The report is working well but if I insert the following formula the whole data disappears: substr (sales rep; 5;10)

It does not matter if I insert the formula to a new column directly or with the help of a variable, After I confirm the formula the sheet is empty.

Can anybody help?

Thanks and kind regards,

Jule