Display of daterange parameter returns an error on BOXI 3.1 R3 Server, but works in Crystal developer 2008

Hi

i have report with a suppresed group header.

That group header shows the date range of the entered date range parameter  (minimum(?date_range) and maximum(?date:range))

When we drill down everything is fine in the crystal developer (version 2008) when we schedule the report on our Business Objects Server (Veersion XI R3) we get an error :

Error in File <Report_name>: Error in formula Display Date Maximum: '//Shows the Maximum date range selected ' Parameter has no value. Details: errorKind

Looks like the parameter is not passed to the group header ?

Can aynone help on that?

regards Alex