Is there an "In/Out" parameter on the stored procedure that returns a Cursor? That is required in order to get the data out of it. Have you tried doing "Verify Database"? If not, I would try that.
Crystal, however, can be very picky about how it handles stored procedures and doesn't always work well when you change them in an existing report. If all else fails, try creating a new report from scratch and see whether you can get the SP fields there.
-Dell