Dear Steve, thanks for your help.
The report works in this way. It reads the field of one table from dictionary which is 1 or 2. This values corresponds to a constant which is "From A" "From B" respectively. When I try to filter the value, the filtering is not working 
do you know what could happen? The definition is type c(20) in every field.....
Thanks again!
Regards,
Rebeca