does changing the selection to single select instead of multi produce better results.
You would think that join to the data table would give the best results...
It's been a long while since I used the parameters, and since anything is possible, is there more than 1000 items in the list? The parameter lists seem to not like displaying more than 1000 rows.
Perhaps CR is getting confused with the data table as values are sure to repeat, but the base lookup table you said yields no results, which seems even odder.
Just for fun (and debugging) you could create a command object like:
select distinct Procedure, code from table
and try using that in the cascading prompts (linking it to the main data table you want to filter). If you get similar results, I would try running the same query on your main datatable...CR will only display parameters for which a report will return results.
So, say you have procedure x, but it is not used in the data table, CR won't list it as a possible parameter as it will return an blank report (at least that has been my experience with cascading parameters)
HTH