Hi,
I think you are trying to use local calculations, if yes, those are not supported in Web Intelligence (not even in the newest release) according to following SAP Note:
Note 1869560 - SAP BusinessObjects BI Support Matrix for SAP NetWeaver BW
If you want to filter out an item from the characteristic structure, then you can easily do this with a block filter (e.g. "Not equal to") on the table, very similar to what is explained in this tutorial:
Web Intelligence 4.0: Set a filter on a section or a block in a document
Best regards,
Victor