i am assuming that by "suppressing a section" that you actually wish to filter these records out of the report..is this correct?
if you are trying to filter out a field that contains '%' then you may not wish to use instr. the reason is that using this function in a filter will not be processed by the database as all records will be returned first to crystal and then filtered out. this will cause performance issues on larger queries.
can you please attach your report with saved data so that we can see what you're trying to do with this prompt / parameter. in order to do this, you must first change the file extension from .rpt to .txt.